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NOTES ON CHEMICAL 
ANALYSIS 


BY 


ARCHIBALD CRAIG, M. A., F. A. I. C. 

> ' 


EASTON, PA. 

THE CHEMICAL PUBLISHING CO. 

1924 


LONDON, ENGLAND: 

WILLIAMS 4 NORGATE, 

14 HENRIETTA 8TREET, COVENT GARDEN, W. C. 


TOKYO, JAPAN! 

MARUZEN COMPANY, LTD., 

11-18 NIHONBA6HI TORI-SANCHOME. 




QU n5 
.C °! 


Copyright, 1924, by Edward Hart. 


MAR 28 1924 


©C1A778612 


'*'• O I 

I 


PREFACE 


It is impossible to write a completely comprehensive text-book 
of analytical chemistry, on account of the infinite variety of con¬ 
ditions governing different chemists in different kinds of work. 
Every chemist makes his own selection of methods for his special 
uses from all the literature that he knows. He depends on his 
own experience so far as possible in judging methods; and when 
that fails, prefers methods that are written by specialists from 
their experience. He avoids the methods which plainly have 
been “only writ for filling, to raise the volume’s price a shilling.” 

The writer, therefore, makes no apology for the fragmentary 
character of this book. It is a collection of things which he be¬ 
lieves to be worth recording, and which have been verified by his 
own experience. He hopes that other analysts may find some 
of his suggestions valuable. 


CONTENTS 


PAGES 

CHAPTER I. 

Glass-working. Apparatus and Tools. Balance and Weights. 
Calibration of Glass Apparatus. Table of Corrections for 
Glass. i -33 

CHAPTER II. 

Tabulation Method for Chemical Calculations. Problems. Cor¬ 
rection for Metallics in Ore Assay. 34~40 

CHAPTER III. 

Some Properties of the Commoner Elements. 41-62 

CHAPTER IV. 

Reagents, Properties and Uses. 63-70 

CHAPTER V. 

Fundamental Operations. Filtering and Washing, Destroying 
Organic Matter, Evaporation. Methods of Decomposition. 

Alloys. Ores, Acid Treatment. Fusion Methods. 71-86 

CHAPTER VI. 

Qualitative Analysis. General Scheme. 87-109 

CHAPTER VII. 

Determinations. 110-128 

CHAPTER VIII. 

Separations. Tin, Antimony and Arsenic. Copper Separations. 

Lead Separations. Bismuth Separations. Cadmium and 

Zinc. Bronze. Aluminium Separations. Uranium Separations. 129-155 










CHAPTER I 


GLASS-WORKING 

Glassware undergoes surface deterioration with age and use. 
This causes roughening, and often cracking, when the glass is 
heated. If the part to be worked is soaked for a minute in a 
mixture of one part HF solution and about ten parts water, 
rinsed in distilled water and dried, it may be softened and welded 
as easily as new glass.* 

The art of glass-blowing consists largely in the ability to hold 
the parts steadily in the flame and to apply the heat equally all 
around. A little practice on scrap tubing, holding one piece in 
each hand and turning it in the fingers or with the wrist, half 
way around, or a trifle more, and back, about two turns to the 
second, will help to give the steadiness necessary for welding. 

Bulbs.—The tube should be heated until the end closes, then 
removed from the flame and blown. When blown in the flame, 
the thinnest part gives way most, and soon breaks into a hole. 
When removed before blowing, the thinnest part becomes hard 
first, while the thicker parts continue to expand. If a large bulb 
is desired, the first small bulb should be heated to thicken it and 
the tube heated farther back and blown, so that more glass is 
included in the bulb. This process may be repeated until enough 
glass has been brought into the bulb. It is then reheated and 
blown slightly until the glass is evenly distributed, and then 
blown to its final size. The turning should continue as long as 
the glass is soft. 

Thistle Tube.—Make a bulb, soften the end of it and burst it 
by blowing suddenly. Crush off the thin edge of the rim thus 
formed and thicken it in the flame. 

Side Hole.—Close one end of the tube with a rubber plug or 
by fusion. Direct a small jet against one spot, while blowing 
gently, until an expansion appears. If a pin hole is required, 
turn the tube so that the flame blows across, not against, the top 
of the expansion, and keep on blowing gently until a break oc¬ 
curs. For a larger hole, soften a larger spot, remove it from the 

* “The Devitrification of Glass.” A. F. O. Germann, J. A. C. S. t Jan., 1921. 


2 


NOTES ON CHEMICAL ANALYSIS 


flame and blow quickly, as in making a thistle tube. Thicken 
the edges in the flame and correct the shape, if necessary, with 
the molding tool. 

Molding Tool.—Grind a stick of arc light carbon to a fine coni¬ 
cal point. It may be used to alter the shape of open ends and 
edges. Hot glass will not stick to it as it does to hot iron or 
platinum. 

Welding Tubes.—The ends of the tubes should be cut off square. 
They should be as nearly as possible of the same composition, so 
that they will have the same rate of expansion and will not crack 
on cooling. If they are not the same size, take the larger piece 
and roughly weld a short piece of rod or tube to it. Heat the 
tube at least half an inch away from the joint, so that the con¬ 
traction will be round, and draw it down to the proper size and 
thickness of wall. The less the glass is pulled in proportion to 
the time and intensity of heating, the thicker the walls will be. 
Cool the piece, scratch it with the glass knife or file, and pull with 
a very light bending stress to crack it off square. Ordinarily, if 
the file or glass knife is sharp, the break will be square. If it is 
not, lay the end on a board with the longer side up and crush 
chips off the edge by bearing down on points near the edge with 
the file or knife. 

Now close all the holes but one of the pieces to be welded, 
except the ends to be joined. If any delicate parts, such as 
stop-cocks, are within two inches of the heat, protect them with 
sheet asbestos or cloth. Fasten a flexible rubber tube about two 
feet long to the extra hole, and hold the end of the tube in the 
mouth. A short piece of glass tube at the end covered with the 
rubber tube makes a good mouth-piece. The extra hole should 
if possible be in the axis of the weld or parallel to it. 

Using a small flame, heat the two ends until they are soft at 
the edges only. Bring them together as accurately as possible, 
advancing them as little as possible to make an air-tight joint. 
The two pieces should be turned back and forth in exact time, 
depending on the adhesion as little as possible to prevent dis¬ 
tortion. If either of the pieces has to be held by a part that 


GLASS-WORKING 


3 


cannot be balanced between the fingers, the turning will have to 
be from the wrist. 

Now bring the flame to bear on one spot of the joint until the 
wrinkles smooth out and the tube begins to collapse. Remove 
from the flame and blow out slightly larger than normal. Allow 
the part to cool slightly and repeat the process in another spot, 
going all around the joint without at any time allowing the entire 
joint to get hot enough to bend easily. 

An expert glass-blower will be able to hold the parts steadily 
enough to heat all around, blow out and draw down to normal in 
one operation. Doing it peacemeal permits the making of a 
durable joint without much skill. When the wrinkles have been 
smoothed out all around, the joint will be slightly larger than 
normal. Heat all around again just enough to soften slightly and 
draw down to normal. 

T-Tube.—Cut two pieces from the same piece of tubing. Heat 
to round the edges of both ends of the longer and of one end of 
the shorter piece. Allow them to cool, stopper the rounded end 
of the shorter tube and one end of the longer. Attach the rubber 
tube to the other end and blow a side hole of about the diameter 
of the tube. Heat the tube enough to soften it for an inch on 
both sides of the tube, and also heat the raw end of the shorter 
tube. The right temperature is shown by the appearance of sodi¬ 
um color in the flame. This will prevent cooling cracks. This 
annealing is not necessary for small tubes of new glass, but for 
large tubes it is a necessary precaution. 

Heat the edges of the hole and the annealed end of the shorter 
tube and bring them together just enough to make an air-tight 
joint. Now bring the flame into the plane of the two tubes, 
bisecting the angle, until the wrinkles in the angle are smoothed 
out, blow out to slightly more than normal size, cool slightly and 
then smooth the other angle. Then smooth the sides, and, if 
necessary go all around again, heating and blowing, until the 
shape is right, but keeping one part cool enough to be stiff to pre¬ 
vent distortion of the tubes. 

A Y-tube is made by bending one tube and blowing the hole at 
the angle before making the joint. 


4 


NOTES ON CHEMICAL, ANALYSIS 


Repairing Broken Ends of Apparatus.—With a pair of sharp- 
edged pliers break off small pieces until the end is square. This 
may be done without cracking if the pliers are held firmly on a 
small part of the edge, without squeezing it, and then twisted 
outward. The thinner the glass and the larger the diameter, the 
smaller the bites must be, and the greater the danger of forming 
cracks. The pressure should not be on two points far apart on 
the outer edge, for fear of splitting the glass downward. If a 
downward crack should form, it may be led around the piece, 
cutting it off square. This is done by heating an iron rod red hot 
and pressing it on the glass near the end of the crack. The crack 
will advance toward the rod, and may be led in any direction. 
Smooth off the rough edge by rubbing it on carborundum cloth. 
If the piece is old, rinse it in HF. Heat it gradually by moving 
it through a white flame until it is covered with soot. Slowly 
turn on the blast, soften the edge, and make a flare or lip with 
the molding tool. 

Ground Joints.—If a ground stopper or cap is lost or one part 
of a tube joint broken, it is not hard to replace it. Choose a 
piece a trifle smaller than the widest part of the ground surface 
if the new piece is to go inside, or a tube that will admit the in¬ 
side piece as far as the ground part if the new piece is to go out¬ 
side. This is to prevent the formation of a shoulder at one end 
of the joint that will confine the grinding to a narrow ring. Then 
draw down the end or give it a flare with the tool, to make it fit 
as nearly as possible, being particular to keep it round. It is 
better to try several times than to grind one that does not fit well. 

The grinding is done by wetting the surfaces and applying 
powdered emery, 6o-mesh or finer. The parts are ground by 
turning, with slight pressure, either in the same direction all 
the time, or else forward and back two or three times and then 
advancing in one direction. This keeps the ground surface 
round. The surfaces should be kept wet and new emery applied 
frequently, until a sufficient band has been ground all around the 
new piece. Now try whether there is a close fit without rocking. 
If it rocks, it is because there has been too much grinding on 
the sides of the band and not enough in the middle. To form a 


GLASS-WORKING 


5 


true conical surface, use very fine emery, either so prepared, or 
that which has been made fine during the grinding. Every two 
or three turns, withdraw the piece and redistribute the emery in 
the joint, so that the largest pieces will grind the most convex 
part and the edges will not touch. The pressure should be very 
light at the end so that the convex part may get all the rubbing. 
Hard pressure, when not exactly straight, will make more grind¬ 
ing on the edges of the ground band, and increase the rocking. 
The joint is finished when it does not rock and when greased 


BAD GOOD 






[ 

Ia 






Fig. i. 


shows a transparent band all around. Fig. i shows good and bad 
work in making the joint. 

Boring Holes in Glass.—This is best done with a three-cornered 
file, mounted in an auger brace. The file should be of the hardest 
steel. The end should be ground off at an angle of 6o° and the 
edges kept sharp by regrinding. It is used like a drill, being 
kept wet with turpentine saturated with camphor. Until the hole 
is cut through, the pressure may be as great as the thickness of 



































6 


NOTES ON CHEMICAL ANALYSIS 


the glass will stand, but as soon as the end breaks through the 
pressure should be lighter to avoid splitting by turning the tool 
while wedged into the hole. After the hole is enlarged as much 
as necessary, or as the size of the drill will permit, it should be 
rounded with a rat-tail file. This is used by turning. The spiral 
grooves in a rat-tail file give it a powerful wedging action if 
turned so as to screw in, and in that way will split the glass. 
Turned against the grooves, the ridges chip out small pieces and 
ream out the hole without danger. 

A hole may be made in glass with a file broken at the end, and 
held in the hand, but this is too laborious for very thick glass. 

In drilling a cover glass, the work is done on the convex side, 
which makes splitting less likely. 

A short piece of rubber tubing may be used to make a tight 
joint with a glass tube in the hole. The rubber must not be 
compressed too much, or it may split the glass. 

APPARATUS 

Filter Rack.—The rack shown is simple in construction, dur¬ 
able and easily carried about. It provides a convenient place for 
rods and cover glasses during filtration, and protects the filtrate 
from spattering. The funnel rests on three points. This makes 
it steady in any position, and the tip may be inclined so as to 
touch the side of any beaker, even if the latter is irregular in 
shape, to prevent splashing of the filtrate. 

The slots make it easy to transfer a funnel from one place to 
another with the beaker under it without stopping the filtration. 

They are also useful when a filtrate needs to be poured back 
for refiltration. The funnel is used as a pouring rod, and the 
operation is quickly performed without danger of losing any of 
the solution. 

A plate should be cut as shown as a pattern for the holes. The 
holes are easily cut with a jig saw, which needs to follow the 
pattern accurately only at the three tangents of the funnel. 
The rack may be made narrow, with six-sided holes instead of 
slots and a ridge on each side to support rods. This form is 
lighter, but has not all the advantages of the slot form. 


GLASS-WORKING 


7 





Fig. 2 . 

A Development of template for notch in rack. 
B Smaller side of notch in C. 

C Funnel raiser. 

D Rack raiser. 















































































































8 


NOTES ON CHEMICAL ANALYSIS 


The rack should be made of light wood that does not warp 
easily, such as white pine. It may be painted, though spar var¬ 
nish is better. Shellac is not durable. 

The sketch shows some extra pieces to be used with the rack. 
The end supports can be set in three positions, to raise the rack 
one, two, or three inches. These supports are also convenient 
supports for round-bottomed flasks. The horseshoe-shaped 



Fig. 3. 

blocks are used to set funnels at different heights. As the sides 
of the slots in the blocks are slanting, two heights may be made 
according to which side is uppermost. The blocks are also used 
to support beakers under the rack. By the use of these extra 
parts filtrations of all sorts can be carried on on the same rack. 










































GLASS-WORKING 


9 


Water System.—Fig. 3 shows a convenient and economical ar¬ 
rangement of water flow. The still should be put in an office, 
or other room free from fumes and dust. The hot water from 
the condenser feeds the water ovens and the water baths, saving 
both heat and water. 

Hydrogen Sulfide Generator.—The generator shown in Fig. 4 
was copied from one at Cornell University. Its advantages are 
cheapness of construction and large capacity. It is easily kept 
clean by turning the hose into it, washing out the insoluble part 
of the iron sulfide. It would be improved by a much taller gen¬ 
erator bottle. The back pressure of the outflow is balanced against 
the head of acid measured from the outlet to the point where the 
bubbles enter the acid bottle. The air inlet needs to turn down 
into a beaker to catch acid occasionally forced out by expansion 
of air in the acid bottle. It is necessary to have sufficient head 
to overcome the high surface tension of the small outlet holes 
and the variations caused by the emptying of the tube just above 
the spray when the flow ceases. The spent acid outlet must be 
high enough to give back pressure when the generator is clean 
and contains only water. Therefore the apparatus works well 
only when made on a large scale, with a generator bottle at least 
eighteen inches high. 

Wash-Bottles.—When water is heated in the bottle, and when 
fuming solutions are used, the Bunsen valve is necessary. This 
may be attached to an ordinary mouth-piece inside the bottle, but 
in this position the rubber rapidly deteriorates, and the tube often 
falls off when in use. The outside valve shown in Fig. 5 lasts 
longer and is not so much affected by the contents of the bottle. 
It may be used for concentrated nitric acid or carbon disulfide. 

By heating the larger end of the outer tube until it has con¬ 
tracted slightly, it is possible to use one piece of rubber tubing 
both for the valve and to seal in the mouth-piece. Rubber is 
best cut while wet. Sharpen a knife with a thin edge, put a 
small stick of wood inside the rubber tube, stretching it slightly, 
and cut against the wood to make a slit with smooth edges. 
Close the end of the tube with a rubber plug, such as is made 


10 



NOTES ON CHEMICAL ANALYSIS 



Fig. 4. 













































































GLASS-WORKING 


II 


by boring a stopper. This will keep its place better than a glass 
plug. 

A convenient insulation of the neck of the wash-bottle may be 
made by wrapping it in several folds of soft paper and covering 
the paper completely with friction tape. Fold the paper into a 
strip of the right width, fasten a piece of tape to the middle of 
the neck and then over the end of the paper strip, to assist in 
winding the paper on solidly. The date marked on the paper so 
that it can be read from the inside will make the bottle last longer. 



A wash-bottle will drip if the outlet tube is too large. Both 
the riser and the tip should be made of thick-walled tubing, of 
not more than four millimeters inside diameter. 

It is important that the tip deliver a straight jet. To make it 
so, draw the tubing slowly, so that it will not become too thin, in 
a regular tapering shape, to the thickness desired for the end. 
Cool the piece, scratch it lightly with a fine sharp-edged glass 
knife or file, and crack it off. If the end is not square, grind 
it square on a piece of fine emery cloth. Wash and dry it, and 













12 


NOTES ON CHEMICAL ANALYSIS 


then round the end in the flame. If the aperture is too large it 
may be made smaller by reheating, but each time it should be 
heated barely to redness, cooled and tested, as it will close rapidly 
when soft. For ordinary work, the jet should be one millimeter 
in diameter. 

Filters.—For filtrations which must be made rapidly, without 
much regard to completeness of washing, the fluted filter is the 
best. This should be set loosely, taking care that the tip is prop¬ 
erly set in the neck of the funnel. If too much expanded the 
paper will fit tightly and cut off the channels. If pressed down 
too far the neck will be plugged. 

The quartered or star filter is popular in colleges. By its 
use rapid filtration may be done with a bad funnel, but it has 
several disadvantages. It takes more time to fold than the ordi¬ 
nary filter. It is almost impossible to keep a column of liquid in 
the stem, so that the speed diminishes as the filter drains, and 
washing is slow. Owing to the inside flaps it is difficult to wash 
a precipitate out of it, which needs to be done in many filtering 
operations. Creeping precipitates are likely to get over it among 
its loose folds. If the filter needs to be reinforced with pulp to 
hold very fine precipitates much of its speed is lost There are 
few cases where it has any advantage over other forms. 

To use the ordinary filter with advantage a good funnel is 
necessary. A funnel should have a regular slope. It need not 
be exactly 6o°, but it should not be bell-shaped or trumpet-shaped 
at the neck. The stem should be not less than three millimeters 
or more than four in internal diameter at any part. This will 
enable bubbles to fill it, and as they go down a suction column 
will be formed. A stem somewhat wider may be used if the 
slope is right, though it is more trouble to start the column and 
it may not be possible to reform it if it breaks. To keep it 
from breaking from below, the tip should be cut square. 

Ten centimeters is an ample length for the stem. A longer 
stem only compacts the precipitate and gives no more speed. 
These dimensions apply to all sizes used for ordinary separa¬ 
tions, up to six inches in diameter. For fluted filters a wide 
stem is better. 


GLASS-WORKING 


13 


For filtering precipitates, fold the paper in half, then with the 
front a little less than a quarter and the back a little more, so 
that the angle between them is 3 0 or 4 0 for a funnel of exactly 
6o°. Tear off a piece one-third as deep as the radius from the 
front corner, using a sidewise twist so that the torn edge is bevel¬ 
led. Open the filter with the wide back layer single, holding the 
front three layers in place with the thumb and finger. Put the 
filter into the funnel, holding the three layers against the side, 
and test the angle The paper should touch at the top and not 
at the bottom. Throw in water around the top, so that it runs 
behind the paper and starts a column, and quickly press the 
paper against the glass all around the top to hold the column. 
When wet, the paper should be free from the glass for the lower 
half of its height, and fit tightly at the top. If the funnel is too 
obtuse or too acute, raise the inner fold and change the angle of 
the paper to suit. 

A filter made in this way takes little more time to set than 
one made carelessly. The speed of filtration continues until 
the filter is empty, making washing rapid. Precipitates do not 
creep over the top. Indeed, many precipitates, such as ferric 
oxide, are perfectly held when the funnel is filled above the 
paper. 

If powdered gangue without any precipitate to bind it is to 
be filtered, as in the analysis of galena, the corner should not 
be torn off, as fine particles will go through the folds. The col¬ 
umn may be secured by pouring a little pulp into the back fold 
and pressing it down. 

Whenever a precipitate is to be washed back for decantation 
or for solution, the smooth inside of the ordinary filter makes 
it preferable to the star filter. The inner fold should be held 
with its edge downward in washing back. 

Pulp.—Many precipitates run through ordinary filter paper at 
first, and when they finally filter clear run slowly. If a little loose 
paper pulp is put into the filter at first these precipitates, such as 
stannic sulfide, can be filtered clear at the start and with less 
clogging of the filter than when it is not used. If the corners 
torn from ashless papers are saved for this purpose, almost 

2 


14 


NOTES ON CHEMICAL ANALYSIS 


enough pulp will be obtained for all filiations, and only one pulp 
flask need be used. Most papers are broken up with difficulty 
by shaking with water in a flask. By adding a few glass beads 
or a rubber stopper, pulp can be made with less work. A whole 
paper is as easily broken up by shaking as when first torn into 
small pieces. 

Some precipitates, such as ferric hydroxide, form hard grains 
when ignited in the ordinary way. If paper pulp is mixed with 
them before filtering, they form fine flaky or powdery residues on 
ignition. In this form they come to constant weight more readily 
and are more easily fused. 

Reinforced Filters.—When very large filters, fifteen centimeters 
or more in diameter, are used, folded in the ordinary way, they are 
likely to break with rough handling. To guard against this, take 
a piece of gauze bandage an inch wide and from one to three 
inches long. Fold the paper in half, lay the cloth over the paper, 
not quite in the middle, but a little toward the wider back part of 
the second fold. Complete the filter as usual. The cloth will 
keep the filter from breaking, enable it to withstand stronger 
acids and alkalies than unsupported paper will, and will make 
filtration faster. 

The Asbestos Funnel Filter.—Wet some glass wool, mold it into 
a ball about the size of a hazel nut, with no long fibres extending 
from it, and pack it into the stem of a funnel, tightly enough to 
keep it in place without choking the stem. Pour in a thin mix¬ 
ture of asbestos until the wool is well covered, and quickly fol¬ 
low this with water, so that a column is formed which will remain 
in the stem after draining. Fibres of glass running through the 
asbestos tend to break the column. Saturate the filter with the 
washing solution before using. 

The Gooch Crucible.—The usefulness of this filter is greatly 
increased by the use of good asbestos and convenient holders for 
the crucibles. Gooch recommended long-fibered asbestos, and this 
kind is still generally used, but it is not necessarily the best. Just 
after the war some asbestos was imported from Italy which ful¬ 
filled every requirement. It was white and clean. When broken 
into short fibers and poured in a milk into the crucible it filled 


GLASS-WORKING 


15 


every hole securely with so little material that the bottom did not 
need to be completely covered, each hole forming a filter by itself; 
and yet the filtration was rapid and ordinary precipitates did not 
run through. The source of this supply is not known, as the lot 
was bought from a jobber, and it has not appeared in the market 
since. In quality it must have been coarser and of more branch¬ 
ing or rougher fibers than ordinary asbestos, though its appear¬ 
ance was the same under a hand glass. 

American asbestos can now be bought of the sort known as 
“Woolly,” a short-fibered by-product of the ordinary mineral, 
which is as rapid as this ideal material. It is not quite white and 
does not make so secure a filter, and more has to be put into the 
crucible to make a reliable mat. However, it can be used in the 
same way, with more care. A pulp of about 1 per cent is shaken 
with water and poured into the crucible with suction, until the 
bottom is just covered. Then the crucible is filled twice and 
sucked dry. Such a pad should weigh from forty to one hun¬ 
dred milligrams. Such precipitates as lead chromate, barium 
sulphate, and magnesium ammonium phosphate can be filtered 
perfectly with full suction on filters made in this way. 

When many Gooch crucibles are used, it is a good thing to 
mark them. 

Roughening Glazed Surfaces.—Precipitate some barium sulfate, 
filter it, and add to the moist pulp an equal volume of hydrofluoric 
acid. With a paddle apply a thick coat of this paste to a square 
on the crucible. Invert the crucible to prevent streaks and let it 
dry. This will make a matt surface suitable for marking with a 
lead pencil. Mark the weight of the crucible to the nearest centi¬ 
gram and a serial number with an A. W. Faber blue pencil No. 
2251 leaving room on the square for lead pencil marks. Burn in 
the marks with the full heat of the blast flame, so that they be¬ 
come dark brown on cooling. If they are only burned red they 
will not be permanent. 

Other glazed utensils, such as silica crucibles and the handles 
of casseroles, should be spotted in the same way so that they can 
be marked easily. 


i6 


NOTES ON CHEMICAL ANALYSIS 


The lower parts of two empty cerusine bottles melted level by 
pressing on a hot plate will make a tight container for the etch¬ 
ing paste. If the edges are pressed together they will adhere. 

Gooch Crucible Holders.—There are several holders on the mar¬ 
ket, but none of them are entirely satisfactory. The holder should 
not collapse or come to pieces when the crucible is removed, 
and it should be possible to remove a crucible and set another 
with one hand without having to readjust the holder. The lower 
part of the crucible should not touch rubber, and the filtrate 
should pass from the crucible into glass without getting into the 
joint between glass and rubber. The crucible should be so held 
that it cannot get wedged into glass under suction, or the glass 
will break. It should be easy to turn the crucible during filtra¬ 
tion, for convenience in washing. 



Gooch’s original form met some of these requirements, but the 
thin rubber band would collapse and it was hard to insert the 
crucible. The glass tube was often broken by the suction. Other 
holders are free from these defects, but they do not allow the 





































GLASS-WORKING 17 

crucible to turn. Fig. 6 shows the form of holder which the 
writer prefers. 

The glass tube fits loosely in the rubber stopper, allowing easy 
turning. It is held down by suction. A bit of tubing below 
the stopper keeps the glass tube in place when not in use. The 
crucible rests on a zone of wide curvature, not quite touching 
the top of the glass tube, so there is no wedging. The glass rises 
high enough around the crucible to keep the filtrate away from 
the rubber band. 

The band may be made from a rubber stopper. Take a piece 
of thin-walled brass tubing, one and one-quarter inches for the 25 
cc. crucible or one and one-quarter for the 35 cc. size. With a 
file sharpen the end to a cutting edge. Select a stopper about 
three-eighths inch larger at the smaller end than the borer, and 
bore a hole through it. Turn the stopper inside out and cut or 
grind a groove about one-quarter inch from the smaller end. 
This groove should have the wall next the smaller end perpen¬ 
dicular to the axis, and should slope away toward the larger end. 
Turn the stopper again and fit it on the glass tube. The groove 
should be deep enough to allow the upper edge of the rubber to 
retain nearly its normal shape. The crucible will then slip in 
easily and be held securely. 

Rubber tubing may be used, but it is hard to get the right size. 
If it is used, the inner edge of the band should be rounded, so 
that the crucible will not catch on it. 

If the rubber tube is used, the holder will fit only one size of 
crucible; but with the bored stopper the glass tube may be wide 
enough to accommodate two sizes; the smaller resting on the bot¬ 
tom and the larger held by the rubber alone. 

The glass tube for this holder may be made to order, or a 
“carbon filter tube” may be cut down to a height which will allow 
the crucible to rest on its bottom. The rubber tubing has a ten¬ 
dency to slip off on account of the narrow zone of contact. It 
may be glued in place by wetting it with strong sodium hydroxide 
solution and allowing it to stand for a week. If the rubber tub¬ 
ing available is not quite wide enough, it may be brought to the 
right size by stretching it over a crucible and heating it in an 
oven. 


i8 


NOTES ON CHEMICAL ANALYSIS 


Ordinarily a flask is used to receive the filtrate, but sometimes 
it is desirable to avoid the dilution from washing out the flask. 
For this purpose a belljar is used, with a beaker. A perforated 
cover glass kept most of the spattering inside the beaker, but 
there is some danger of loss. Spattering may be prevented by 
the side-opening belljar shown in Fig. 6. If the crucible holder 
touches the side of the beaker the filtrate will drain quietly, 
though the beaker is easily displaced if the crucible is turned in 
washing. If the tip is enclosed in a tube of about one centimeter 
inside diameter, resting on the bottom of the beaker, splashing 
is prevented. A notched cover may be used. 



Tools for Handling Apparatus.—Fig. 7 shows a holder which is 
convenient for lifting crucibles containing liquid. The crucible 
rests on three points and cannot rock. The solid fork is more 
reliable than forceps, as it will not touch a cover on the crucible, 
will not slip, and protects the hand from the heat of the stove! 
There is a possibility of tilting the crucible by lifting while the 
fork touches the crucible only at the sides and not at the back, 
but with care this may be avoided. Forks of this shape with the 
handles turned up more may be used to transfer covered crucibles 
to dessicators. 








GI^ASS-WORKING 


19 


Fig. 8 shows wooden tongs for flasks. They should be made 
of hard wood. The hinge should have a close-fitting pin, or it 
may be made of spring metal or leather. A glass tube may fie 
mounted on a pair of tongs, so shaped as to direct a jet of air 




into the flask for rapid evaporation. The spring should be just 
strong enough to keep them open when held empty in the hand. 

Fig. 9 shows beaker tongs. The grip of these tongs is not a 
simple V, but a compound curve, designed to give the maximum 
contact surface to beakers of all sizes from 100 cc. to 1,000 cc. 
The contact surface is extended by flattening the metal on the 
inside and by covering it with thick rubber tubing. 

The handles are about as long as the grip, so the force re¬ 
quired to hold a beaker is about the same as for holding it in the 
hand. No new habit needs to be learned in using them, and there 
is no danger of crushing beakers by holding them too tightly. 
They are real fire-proof fingers. A large beaker full of water 
may be held and carried by the middle, solutions may be shaken 








20 


NOTES ON CHEMICAL ANALYSIS 


or rotated, and beakers may be tilted for pouring as easily and 
securely as though held in the hand. They are particularly 
convenient for pouring hot acids. 



It is convenient for the chemist to carry his tongs in a pocket, 
so as to have them ready for emergencies and to save the trouble 
of hunting them when needed in different parts of the laboratory. 
One pair for each chemist is a complete outfit. 

These tongs are sold as the “Craig Beek-tong. ,, 

Rubber Stoppers.—Only solid stoppers should be bought for 
laboratory use, as the holes in those bought perforated seldom 
fit the tubing used in apparatus. 

The cork borers should be kept sharp with the special sharp¬ 
ener. A slight variation in bore may be made by changes in 
the cutting edge. If the borer is pressed hard against the cone 
of the sharpener and the knife pressed lightly, an outward flare 
is produced which makes a hole slightly larger than normal. By 
holding the borer lightly against the cone, inclined away from the 
knife, and pressing hard on the knife, the edge is crimped, pro¬ 
ducing a smaller hole. 

The cores obtained by boring the stoppers are useful. A 
rubber plug made from one of them is better than glass in a 
Bunsen valve, as it never drops out. 

When a tube is left in a beaker during boiling, the liquid is 
likely to be shot out by steam. A rubber core tapered with a 
knife or on an emery wheel makes a good plug. 

Boring in rubber, as well as cutting with a knife, is easier if 
the surfaces are kept wet. Much turning and little pressure 
makes a smooth full-size bore. 







GLASS-WORKING 


21 


A stopper which is used in distilling quickly takes the form 
into which it is compressed while hot, the holes enlarging to 
the size of the glass tubes. If the holes are cut in the first place 
approximately the size of the tubes there will be less distortion 
of the stopper after heating, and the fit will be as close as though 
the tubes had been forced into smaller holes. 

Ordinary stoppers distil H 2 S on the first heating with acid. 
Stoppers are made without sulfur, which are free from this 
defect. Stoppers bearing the brand E & A “Sulfree” have the 
added advantage of being less altered by heat than the ordinary 
kind, and their greater durability more than pays for their extra 
cost. 

Policemen.—A convenient and durable policemen can be made 
from a rubber stopper or other piece of pure rubber. Take a 
No. i stopper and a glass rod about four-tenths by twenty centi¬ 
meters. Bore a hole slightly smaller than the rod half way 
through the stopper from the smaller end. If the boring is done 
dry, friction may cause the core to break off in the borer at 
about the right place. If it does not, pull the core out with for¬ 
ceps. Wet the rod with concentrated NaOH solution and set it 
in the hole. In about a week the glass and rubber will be firmly 
cemented together. 

Cut the larger end of the stopper into a wedge, taking care 
not to cut too close to the glass rod. Smooth the surfaces into 
a chisel edge on an emery wheel or cloth. 

The best motion in cleaning a beaker with this policeman is 
up and down so that water is brought up on the sides at each 
stroke. 

Marking on Glass and Porcelain.—A. W. Faber blue pencil No. 
2,251 makes a good mark on glass, particularly if the surface is 
warm. It is particularly good for porcelain crucibles, as it does 
not run when heated, but leaves a red residue of ferric oxide. 
This may be made permanent by heating strongly in the blast 
flame. 

Blaisdell red pencil No. 169 makes a good mark on glass which 
does not run when heated, but it burns off. 

Both marks are easily removed with Gresolvent. 


22 


NOTES ON CHEMICAL, ANALYSIS 


A cheap lead-pencil containing much clay is useful for iron 
and the rough bottoms of porcelain crucibles. A legible mark 
remains after ignition. 

A recent Blaisdell product, brown laboratory pencil, No. 266 
makes a permanent mark when burned. It runs when heated. 
Probably this defect will soon be remedied by the use of a suit¬ 
able coagulant. 

Pouring Bottle.—Fig. 10 shows a pouring bottle, particularly 
suited for ammonia. If the tip is made with care and the bore 




Fig. 11 . 


is two to two and five-tenths millimeters, it may be used like a 
Gay-Lussac burette, either for pouring or for dropping. In neu¬ 
tralizing acids with ammonia less fume is produced than when 
an ordinary bottle is used, and the last drops are more easily 
controlled. 



















GLASS-WORKING 


23 


Mouth-Piece.—When several chemists use special solution 
wash-bottles in common, private mouth-pieces are used. The one 
shown in Fig. 11 keeps the tube from touching the table when it 
is not in use. The tube is large enough to accommodate the 
largest wash-bottle tube, and the bore of the squared stopper is 
smaller than the tube, so that the bore of the tube is tapered to 
fit smaller wash-bottle tubes. 

Flask Cover.—Fig. 12 shows a device for evaporating solu¬ 
tions from flasks. By keeping the entire flask warm, condensa¬ 
tion on the sides is prevented, and evaporation proceeds at a 



low temperature. By its use heavy liquids may be evaporated 
without bumping. The cover may be made from a tin can, but 
it is worth while to have it made higher and narrow, so that the 
neck can be covered and the diameter suited to the flasks used. 

Dipping Pipette.—Fig. 13 shows an arrangement for measur¬ 
ing out reagents. The cover is made of a watch-glass or the lining 















24 


NOTES ON CHEMICAL ANALYSIS 


of a Mason jar lid. The pipette is kept in place by a piece of 
rubber tubing if the reagent does not attack it. Otherwise the 
tube of the pipette may be blown into a small bulb just below the 
cover and a glass ferrule kept in place above it by a rubber tube 
or sealing wax some distance above the cover. 





If the pipette is used without the cover, resting on the bottom 
of a bottle, it is important to pick a bottle like A and not like B, 
as the latter will catch the end of the pipette and break it. 

The only important dimension of the pipette is the aperture, 
which should be as large as the surface tension of the liquid 
will permit, for speed in delivery. For H 2 ,S 0 4 the aperture 
should be five millimeters for any size pipette. For HNO s and 
water solutions it may be as large as six millimeters. 



























GLASS-WORKING 


25 


The Chemical Balance.—The greatest variations in the adjust¬ 
ment of a balance come from dirt on the beams and hangers. 
Aluminium particularly becomes corroded, and the oxidized parts 
are hygroscopic, holding different amounts of water at different 
temperatures. Whenever the temperature of the room changes, 
if the beam is dirty, the balance has to be readjusted. 

Bronze beams are less subject to this variation, but it is worth 
while to keep the beam and hangers smooth and bright. 

Some balances are equipped with two rider arms, so that one 
rider can be used for weighing and the other to adjust, instead 
of the nut at the end of the beam. Adjusting by the rider re¬ 
quires fewer motions, as by observing the difference in the swing 
the rider can be moved in most cases to the proper place at the 
first trial. 

An adjusting rider can be used on an ordinary one-arm bal¬ 
ance by reversing the left side hook, so that when one hook is in 
use the other extends backward, and only one can be lifted at a 
time. The extra time taken by setting the weighing rider on 
the beam while moving the adjusting rider, and lifting it after¬ 
ward is more than made up by avoiding the air currents set up 
by putting the hand into the balance. 

Speed in weighing is gained by setting the pan rest a little 
out of level, so that when it is released the needle swings a defi¬ 
nite distance more than the difference in weight would cause. 
When the balance is in good condition and in adjustment, the 
needle will start from rest when the pan rest is lowered, and will 
swing exactly as far on the other side. It is therefore possible 
to read the needle on the half swing, instead of allowing it to 
return. By setting the pan rest so that the needle rests at an 
even division, one or two by preference, and knowing how far 
a milligram will carry it, the rider may be set by reading the 
needle to the half swing with sufficient accuracy to allow a bal¬ 
ance in two trials after the difference has been reduced to a 
milligram or so. 

In order to read the half swing, it is necessary to have the 
pan rests in good condition, so that there will be no “kick” when 


26 


NOTES ON CHEMICAL ANALYSIS 


they are lowered. The pads should be clean and composed of 
the same material, so that both may have the same elasticity 
and neither will stick to the pan. 

Some saving in adjustment time can be gained by having a 
watch-glass on the pan all the time. A flat plate, either of metal 
or glass, instead of another watch-glass, should be used as a 
counterpoise on the weight side, so that the weights can be ar¬ 
ranged in order without their sliding into a heap. A camera dry 
plate is about the right thickness so that a piece cut from it 
heavy enough to balance a watch-glass will cover the pan. A 
rectangular plate is better than a round one, as the weights can 
be arranged better on it. It is not necessary to get an exact 
counterpoise between the two pieces. By making the flat plate 
slightly lighter the difference can be made up by a piece of lead 
foil laid under the plate. 

It is convenient to keep, the fractional weights on a card glued 
to the floor of the balance pan. If the card is made of thick 
pasteboard a shallow wooden box with one side removed may be 
slid over the weights to protect them. The card should be 
marked in rectangles with a place for each weight. If the 
weights are then placed on the balance pan in the same relative 
places as on the card, they may be read more easily and accu¬ 
rately than if placed at random on the pan. 

Adjusting Weights.—The ordinary analytical weights consist 
of brass for one gram and over, platinum or a gold alloy for 
fractional weights of five-hundredths gram and over, and alum¬ 
inium for those under five-hundredths. 

The brass weights are kept to standard by changing the loose 
material in the cavity opened by unscrewing the handle. They 
should be rubbed with a dry cloth until smooth before adjusting, 
allowing any oxide that may have formed on exposed spots to 
form a protective coating, rather than trying to clean the bare 
metal. 

Platinum weights can be made up to standard when light by 
the addition of gold. The weight should first be cleaned in al¬ 
cohol and ether, using a match-stick cut to a chisel edge to 


GLASS-WORKING 


27 


loosen dirt. It should then be heated to redness, held with plati¬ 
num-tipped forceps. 

A pair of brass forceps may be tipped with pieces of platinum 
foil at small expense. The brass tips should be filed to parallel 
sides, so that rectangular pieces of foil can be tightly wrapped 
around them. The foil should extend about five millimeters be¬ 
yond the brass. By closing the forceps tightly and pressing the 
two hollow extensions together with pliers, satisfactory tips can 
be made. The seam should be at the outside of the forceps, and 
may be soldered with a very small piece of solder, taking care 
not to allow the solder to spread to the front. 

After the weight has been cleaned it should be compared 
with the standard and enough gold to make up the difference 
placed on it, preferably in the hollow of a figure, and held in 
the platinum forceps over a small blast flame until the gold 
melts and fuses into the platinum. The easiest way of getting 
an accurate check is to make the weight slightly heavy and then 
rub off the excess on a sheet of very fine emery paper, such as 
is used for polishing metal. 

Gold and German silver weights can be spotted in the same 
way with tin. Silver may be used to spot gold weights if care 
is used to control the heat. 

Aluminium weights are best cared for by rubbing enough 
dirt off with a stick to bring them to standard, and when too 
much worn, discarded. 

Calibration and Use of Burettes.—In the use of burettes it is 
often directed to run out the solution rapidly and then wait a 
specified time for the sides to drain to a constant level before read¬ 
ing. The objections to this are, that the level of the solution in 
the burette rises more slowly as the drainage approaches zero 
and the operator is tempted to read too soon; that the proper 
drainage time varies with the height of column to be drained; 
that the solution evaporates more or less during the drainage and 
the reading is not exact; and that waiting for the burette to settle 
is an exasperating delay and consumes more time than regulating 
the flow. 


28 


NOTES ON CHEMICAL ANALYSIS 


By properly regulating the flow, the burette will drain itself 
as it empties, and can be read at once, the level remaining con¬ 
stant from the moment the flow ceases. The maximum rate 
which gives perfect drainage is within the limits which can be 
used for calibration, and a slight increase over this can be used 
in titrations without appreciable error, so that the burette can 
always be read as soon as the stop-cock is turned. 

A burette should be so made that twenty drops make I cc. 
For calibration the rate of flow should be such that the water 
breaks into drops at the tip. For titrations the speed may be 
increased so that a continuous stream is half an inch long be¬ 
fore breaking into drops. This will make a slight difference in 
the delivery of the burette, but not in the ratio of its parts, and 
if the solutions are standardized at the same rate of flow that 
is used for determinations, there will be no error. This rate 
is fast enough for most titrations, as the standard solution ought 
to be well mixed as it runs in, and if it runs too fast there may 
be an error. This is particularly true of iodine titrations. 

A convenient way to calibrate a burette is to have a beaker 
of water of room temperature, with an accurate thermometer in 
it, and a long-necked flask just large enough to receive the water 
from the burette. The burette should be so supported that it 
can be read without moving it. 

Weigh the flask, run in io cc., weigh, and so to the bottom. 
Refill the burette and weigh the full delivery at once. The two 
results should agree within five-hundredths gram. 

Pipettes are calibrated in the same way, by weighing the 
delivered water in a flask. As solutions of varying viscosity and 
density are used in pipettes, experiments should be made to 
determine the delivery of different kinds of solutions in common, 
use. The delivery of a pipette depends somewhat on the method 
of touching off the drop at the end of the delivery. The Bureau 
of Standards method of touching off the drop as soon as the 
flow ceases, on the surface of the liquid or, better, on the wet 
side of the container, is the quickest and most practical. 

Burettes should be tested when bought, and those not suffi¬ 
ciently accurate sent back. Flasks and pipettes can be made more 


GLASS-WORKING 


2 9 


accurate than they ordinarily are when bought ready made by 
buying them unmarked, calibrating them and sending them back 
to have the marks etched in. 

The temporary mark is best made with black shellac. A glass 
rod drawn to a thread and wet with the shellac makes a good 
marker. In all such work a perfectly level table should be used, 
and a sight taken from the horizon or from a level mark on a 
window. Pipettes should be held in the hand against a frame 
which will hold them vertical. 

The accompanying tables of corrections are taken from Cir¬ 
cular 19 of the U. S. Bureau of Standards, entitled “Standard 
Density and Volume Tables.” 

Tables of corrections for determining the true capaci¬ 
ties of glass vessels from the weight of water in air, 
using brass weights. They give the capacities in cubic 
centimeters at 20° C., barometric pressure seventy-six 
centimeters, relative humidity 50 per cent, coefficient 
of expansion of glass 0.000025 per degree C. 


Indicated Capacity 250 ml. 


Temp. 




Tenths of degrees 




Deg. C. 

0 

1 

2 

3 

4 

5 

6 

7 

_ 8 _ 

9 

15 

0.518 

0.521 

0.524 

O.527 

0.530 

0-534 

0-537 

0.540 

0-543 

0.546 

16 

•550 

•554 

•557 

.560 

.563 

.567 

•570 

•574 

•578 

.581 

17 

.584 

.588 

•592 

.596 

.600 

.603 

.606 

.6lO 

.614 

.618 

18 

.622 

.626 

.630 

.634 

.638 

.642 

.646 

.650 

.654 

.658 

19 

.662 

.666 

.670 

.674 

.679 

.683 

.687 

.692 

.696 

.700 

20 

705 

.709 

.714 

.718 

.722 

727 

•732 

736 

•741 

.746 

21 

•750 

•754 

.760 

.764 

.769 

•774 

.778 

.784 

.788 

•793 

22 

.798 

.803 

.808 

.813 

.8l8 

.824 

.828 

.834 

.839 

.844 

23 

.849 

.854 

.860 

.865 

.870 

.875 

.881 

.886 

.892 

.897 

24 

.902 

.908 

.913 

.919 

.924 

•930 

.936 

•941 

•947 

•952 

25 

•958 

.964 

.969 

•975 

.981 

.986 

.992 

.998 

1.004 

I.OIO 

26 

I. 0 I 6 

1.022 

1.028 

1.034 

1.040 

I.O46 

1.052 

1.058 

1.064 

1.070 

27 

1.076 

1.082 

1.089 

1.095 

I.IOI 

1.108 

I.II 4 

1.120 

1.126 

1.132 

28 

1139 

1.146 

1.152 

1.158 

1.165 

1.172 

1.178 

1.184 

1.191 

1.198 

29 

1.204 

1.211 

1.218 












30 


NOTES ON CHEMICAL, ANALYSIS 


Indicated Capacity 200 ml. 

Temp. Tenths of degrees_ 


01 

Deg. C. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

15 

0.414 

0.417 

0.419 

0.422 

0.424 

0.427 

0.430 

0.432 

0.435 

0.437 

l6 

•440 

443 

•445 

.448 

•451 

.454 

456 

•459 

.462 

.465 

17 

.468 

.470 

473 

477 

•479 

.482 

.485 

.488 

.491 

•494 

18 

•497 

.501 

.504 

.507 

.510 

•513 

.516 

.519 

.523 

.526 

19 

.529 

•533 

.536 

•540 

•543 

.546 

•550 

•553 

•557 

.560 

20 

.564 

•567 

•571 

•574 

.578 

.582 

.585 

.589 

•593 

.596 

21 

.600 

.604 

.608 

.612 

.615 

.619 

.623 

.627 

.631 

.635 

22 ’ 

.639 

.643 

.647 

.650 

.655 

.659 

.663 

.667 

.671 

.675 

23 

.679 

.683 

.688 

.692 

.696 

.700 

.705 

.709 

.713 

.717 

24 

.722 

.726 

•731 

•735 

•739 

•744 

.748 

•753 

•757 

.762 

25 

.766 

.771 

•775 

.780 

.785 

.789 

•794 

•799 

.803 

.808 

26 

.813 

.818 

.822 

.827 

.832 

.837 

.842 

.846 

.851 

.856 

27 

.861 

.866 

.871 

.876 

.881 

.886 

.891 

.896 

.901 

.906 

28 

.911 

.917 

.922 

.927 

•932 

•937 

.942 

•947 

•953 

.958 

29 

.963 

.969 

•974 









Indicated Capacity 150 ml. 


Temp. 




Tenths of degrees 




Deg. C. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

15 

0.311 

0.313 

0.314 

O.316 

0.318 

0.320 

0.322 

0.324 

O.326 

0.328 

l6 

•330 

•332 

•334 

.336 

•338 

•340 

.342 

•344 

.346 

•349 

17 

•351 

•353 

•355 

•357 

•359 

.362 

.364 

.366 

.368 

•371 

18 

•373 

•375 

•378 

.380 

.38 3 

.385 

.387 

•390 

•392 

•395 

19 

•397 

.400 

.402 

405 

.408 

.410 

.412 

415 

.418 

.420 

20 

.423 

.425 

.428 

•431 

•433 

436 

•439 

442 

•445 

.448 

21 

•450 

•453 

456 

•459 

.461 

.464 

.467 

•470 

•473 

476 

22 

•479 

483 

485 

.488 

.491 

•494 

•497 

.500 

.503 

.506 

23 

.509 

.512 

.516 

.519 

.522 

.525 

.529 

•532 

•535 

.538 

24 

.541 

•545 

.548 

•551 

•554 

.558 

.562 

.565 

.568 

•571 

25 

•575 

.578 

.581 

.585 

.588 

•592 

.596 

•599 

.602 

.606 

26 

•6l0 

.613 

.617 

.620 

.624 

.628 

.631 

.635 

.638 

.642 

27 

.645 

.649 

.653 

.657 

.661 

.664 

.668 

.672 

.676 

.680 

28 

29 

.684 

.722 

.688 

.726 

.691 

.730 

.695 

.699 

.703 

.707 

.711 

.715 

.719 



























GLASS-WORKING 


31 


Indicated Capacity ioo me. 


Temp. 

in 




Tenths of 

degrees 





Deg. C. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

15 

0.207 

0.208 

0.210 

0.211 

0.212 

0.213 

0.215 

0.2l6 

0.217 

0.219 

16 

.220 

.221 

.223 

.224 

.225 

.227 

.228 

.230 

.231 

.232 

17 

.234 

•235 

.2 37 

.238 

.240 

.241 

•243 

.244 

.246 

.247 

18 

.249 

.250 

.252 

•253 

•255 

•257 

.258 

.260 

.261 

.263 

19 

.265 

.266 

.268 

.270 

.272 

•273 

•275 

•277 

.278 

.280 

20 

.282 

.284 

.285 

.287 

.289 

.291 

•293 

.294 

.296 

.298 

21 

.300 

.302 

•304 

.306 

.308 

.310 

.312 

.314 

.315 

.317 

22 

.319 

.321 

•323 

.325 

.327 

.329 

•331 

•333 

.336 

.338 

23 

•340 

•342 

•344 

.346 

.348 

•350 

•352 

•354 

•357 

•359 

24 

.361 

.363 

•365 

.368 

•370 

.372 

•374 

.376 

•379 

.381 

25 

.383 

.386 

.388 

•390 

•392 

•395 

•397 

•399 

.402 

.404 

26 

.406 

.409 

.411 

.414 

.416 

.418 

.421 

.423 

.426 

.428 

27 

.431 

•433 

•436 

.438 

.440 

•443 

.446 

.448 

•451 

•453 

28 

456 

•458 

.461 

463 

.4 66 

.469 

•471 

•474 

.476 

•479 

29 

.482 

.484 

.487 











Indicated Capacity 50 me. 



• 

Temp. 




Tenths of degrees 





Deg. C. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

15 

0.104 

0.104 

0.105 

0.106 

0.106 

0.107 

0.107 

0.108 

0.109 

0.109 

16 

.110 

• III 

.111 

.112 

.113 

•113 

.114 

•115 

.Il6 

.116 

17 

• 117 

.Il8 

00 

HH 

hH 

.119 

.120 

.121 

.121 

.122 

.123 

.124 

18 

.124 

.125 

.126 

.127 

.128 

.128 

.129 

.130 

.131 

.132 

19 

.132 

.133 

•134 

.135 

.136 

•137 

•137 

.138 

•139 

.140 

20 

.141 

.142 

•143 

.144 

.144 

•145 

.146 

.147 

.148 

.149 

21 

.150 

.151 

.152 

•153 

•154 

•155 

.156 

•157 

.158 

• 159 

22 

.160 

.l6l 

.162 

.163 

.164 

.165 

.166 

.167 

.168 

.169 

23 

.170 

.171 

.172 

• 173 

.174 

•175 

.176 

•i 77 

.178 

.179 

24 

.180 

00 

l-l 

.183 

.184 

.185 

.186 

.187 

.188 

.189 

.190 

25 

.192 

.193 

• 194 

.195 

.196 

.197 

.199 

.200 

.201 

.202 

26 

.203 

.204 

.205 

.20 7 

.208 

.209 

.210 

.212 

•213 

.214 

27 

•215 

.216 

.218 

.219 

.220 

.222 

.223 

.224 

.225 

.226 

28 

.228 

.229 

.230 

.232 

.233 

•234 

.236 

•237 

.238 

.240 

29 

.241 

.242 

.244 


































32 


NOTES ON CHEMICAL ANALYSIS 


Indicated Capacity 40 ml. 


Temp. 




Tenths oi 

: degrees 





in 

Deg. C. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

15 

0.083 

0.083 

0.084 

O.084 

0.085 

0.085 

0.086 

0.086 

0.087 

0.087 

16 

.088 

.089 

.089 

.090 

.090 

.091 

.091 

.092 

.092 

•093 

17 

.094 

.094 

•095 

•095 

.096 

.096 

.097 

.098 

.O98 

.099 

18 

.099 

.100 

.101 

.101 

.102 

.102 

.103 

.104 

.105 

.105 

19 

.106 

.107 

.107 

.108 

.109 

.109 

.110 

.111 

.III 

.112 

20 

• 113 

.113 

.114 

.115 

.Il6 

.Il6 

.117 

.118 

.119 

.119 

21 

.120 

.121 

.122 

.122 

.123 

.124 

•125 

.125 

.126 

.127 

22 

.128 

.129 

.129 

.130 

.131 

.132 

.133 

• 133 

•134 

.135 

23 

.136 

• 137 

.138 

.138 

•139 

.140 

.141 

.142 

.143 

.143 

24 

.144 

■ 145 

.146 

•147 

.148 

.149 

.150 

.151 

.151 

.152 

25 

• 153 

• 154 

.155 

.156 

.157 

.158 

•159 

.160 

.l6l 

.162 

26 

.163 

.164 

.164 

.165 

.166 

.167 

.168 

.169 

.170 

.171 

27 

.172 

.173 

•174 

.175 

.176 

.1 77 

.178 

.179 

.l80 

.l8l 

28 

.182 

.183 

.184 

.185 

.l86 

.187 

.188 

.189 

.191 

.192 

29 

.193 

.194 

.195 











Indicated Capacity 30 ml. 




Temp. 




Tenths of degrees 




Deg. C. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

Q 

15 

0.062 

0.063 

0.063 

O.063 

O.064 

0.064 

O.064 

0.065 

0.065 

0.066 

16 

.066 

.066 

.067 

.067 

.068 

.068 

.068 

.069 

.069 

.070 

1 7 

.070 

.071 

.071 

.071 

.072 

.072 

•073 

.073 

.074 

.074 

18 

.075 

•075 

.076 

.076 

•o 77 

.077 

•o 77 

.078 

.078 

.079 

19 

.079 

.080 

.080 

.08l 

.081 

.082 

.082 

.083 

.084 

.084 

20 

.085 

.085 

.086 

.086 

.087 

.087 

.088 

.088 

.089 

.089 

21 

.090 

.091 

.091 

.092 

.092 

•093 

•093 

.094 

•094 

•095 

22 

.096 

.096 

.097 

.O98 

.098 

.099 

.099 

.100 

.IOI 

.101 

23 

.102 

.103 

.103 

.104 

.104 

.105 

.106 

.106 

.107 

.108 

24 

.108 

.109 

.110 

.110 

.111 

.112 

.112 

.113 

.114 

.114 

25 

• 115 

.116 

.116 

.117 

.118 

.118 

.119 

.120 

.121 

.121 

26 

.122 

.123 

.123 

.124 

.125 

.126 

.126 

.127 

.128 

.128 

27 

.129 

.130 

.131 

.131 

.132 

.133 

•134 

.134 

•135 

.136 

28 

.137 

• 137 

.138 

.139 

.140 

.141 

.141 

.142 

.143 

.144 

29 

• 145 

.145 

.146 


































GLASS-WORKING 


33 


Example of Use of Table.—Determination of the capacity of a 
glass measuring flask marked “to contain 250 milliliters at 20° 

C.” 


Apparent weight of water at the observed tem¬ 
perature 22.3 0 C.249.198 g. 

Correction from table . 0.813 


Actual capacity in ml. or cc. at 20° . .. .250.011 





CHAPTER II 


TABULATION METHOD FOR DIRECT RATIOS 

This method is useful for chemical calculations, in which most 
ratios are direct. It furnishes a convenient scheme for record¬ 
ing data and results, and serves as a guide to the solution of 
problems. 

Rule 1 .—In any problem, make a series of columns, heading 
each with the name of a kind of quantity, so that all quantities 
of the same kind shall be in the same column. 

Rule 2 .—Quantities in the same horizontal line must be 
known to have a constant relation to each other. All must be 
facts which are at the same time true in a particular case, ex¬ 
pressed in quantities described by the column headings. 

Rule 3 .—If any four quantities in different parts of the chart 
form a rectangle, the product of two diagonally opposite corners 
is equal to the product of the other two comers, by proportion. 

If three corners of a rectangle are filled the fourth may be 
found by multiplying the pair of diagonals and dividing by the 
third, as in proportion. 

Rule 4 .—Rectangles may be filled in any order, beginning with 
one having three known quantities, but there is often economy 
of attention and work in filling corners on the same line, either 
horizontal or vertical, with the position of the desired result. 

Rule 5 .—Before beginning the calculation, tabulate all data 
relating to the problem, allowing space for additions and sub¬ 
tractions due to back titrations and similar procedures in which 
the algebraic sum of two or more quantities is the measure of 
the element to be determined. 

Locate on the chart the position of the desired result, and 
mark it with braces (). Then mark the position which must 
be filled in order to have three known quantities in a rectangle 
with the position of the result, making as few steps as possible. 

Fill the rectangles by calculation, beginning with the one which 
has three comers filled. 


TABULATION METHOD FOR DIRECT RATIOS 35 

Rule 6.—The calculation may be checked by filling rectangles 
not used in the first solution until the desired position has been 
reached. 

Rule 7 .—Any problem or part of a problem in which there are 
no additions may be solved by logarithms. Locate all the rec¬ 
tangles necessary to the solution. Take the first rectangle, set 
down the logarithms of the diagonals and the cologarithm of 
the odd corner. The sum of these gives the logarithm of the 
fourth corner. Take the next rectangle containing this corner, 
put down in the column the logarithm of its diagonal and the 
cologarithm of its vertical or horizontal mate. The sum is the 
logarithm of the fourth corner of the second rectangle. Pro¬ 
ceed in this way until the result has been reached, solving for 
it alone, or for all the intermediate quantities, as desired. 

In the examples, the data found by observation are under- 
scored. All quantities obtained from other sources, such as 
handbooks, are marked by “quotes.” Quantities obtained by cal¬ 
culation in the first solution are enclosed in (braces). The 
second line of calculation is left unmarked. In actual use, only 
the braces need be used. 

Example 1 .—How many cubic centimeters of nitric acid, 69.8 
per cent pure, specific gravity 1.42, will make a liter of normal 

solution ? 


Cc. normal 
solution 

Grams pure HN 0 3 

Grams reagent HNO3 

Cc. reagent HNO a 

“1,000 

63.018” 

90.28 

( 63 . 58 ) 

63.58 

15 . 728 ” 

(0.99116) 

“I.42 

I” 


69.8” 

IOO” 



By definition, a liter of normal acid contains one hydrogen 
equivalent, in this case one gram molecule. Specific gravity in 
the metric system is numerically the same as density, the weight 
in grams of one cubic centimeter. The expression “69.8 per cent 
pure” means that 100 parts by weight of a given material con¬ 
tains 69.8 parts by weight of the pure substance named. Both 
percentage and specific gravity are ratios, and each is expressed 
by two quantities in different columns. 



















36 


NOTES ON CHEMICAL ANALYSIS 


The preferred solution of this problem does not follow Rule 4, 
because the intermediate step showing grams HNO s per cc. is 
itself a useful figure. Incidentally the normal strength of the 
reagent, 15.728, is easily found. 

Example 2 .—In the reaction 3 SnCl 2 -f- 4 HC 1 -f- KC 1 Q 3 = 
KC 1 3 SnCl 4 +2 H a O, how many grams of KC 10 3 will be 
required for 5 grams of Sn, and how many cc. of reagent HC 1 , 
37.23 per cent pure, specific gravity 1.19, will be neutralized? 


Grams Sn 

Grams HC 1 

Grams KC 10 3 

Grams 
reagent HC 1 

Cc. reagent HC 1 

5 

(2.0434) 

(I.7I7) 

(54.89) 

(4.61) 4-6r 

“357 

145 . 90 ” 

122.56” 


329.3 




‘‘1.19 

I” 


“37.23 


loo” 

81.04 


Here the multiples of the molecular and atomic weights are 
obtained from the coefficients in the equation. As these may be 
expressed in any unit, it is legitimate to put them in the same 
column with grams actually weighed. 

Example 3 .—A sample of commercial sulfuric acid was as¬ 
sayed as follows. Having some solutions approximately 0.2 N 
NaOH and 0.5 N HC 1 , they were titrated against each other and 
against Na 2 C 0 3 . To titrate the sample, some of it was weighed 
into a beaker, slightly less than its equivalent of Nau>C0 3 was 
weighed into it, the C 0 2 boiled out, and the excess titrated with 


Cc. NaHO 

Cc. HC 1 

Grams 

Na 2 C 0 8 

Cc. normal 

Grams 

sample 

Grams 

h 2 so 4 

Grams 

Fe 2 Os 

Grams 

ZnO 

(89.55) 

36.70 

1.0013 

(18.892) 





34.40 

10.00 







4.7402 

1 9427 

“0.00530025 

1” 


0.049043” 

0.0266” 

0.0407” 

(«> 



(0.2110) 

0.2110 


0.010348 




(1) 


00*00 

m * 

6 6 





1320 


4.0507 

+ 2.785 

+76.425 

— 0.241 

— 0.074 

78.895 

5 - ii 75 

(+0.1366) 

(+3.7481) 

(—0.0118) 

(—0.0036) 

( 3.8692) 

0.0064 

0.0030 





"100" 

( 75 - 6 i) 



















































TABULATION METHOD FOR DIRECT RATIOS 


37 


NaOH. After titrating a precipitate was found, the bases in 
which were originally combined with the acid, making it necessary 
to deduct their acid equivalents from the titration figure in order 
to show the free acid. All the data were referred to H 2 S 0 4 . 
As a check, the data were referred to normal solution. 

Example 4 .—A sample of copper was assayed for S by con¬ 
version to H 2 S in a stream of H and titration with iodine by the 
reaction H 2 S + 2 I = 2 HI -f- S. On a 95-gram sample 0.35 cc. 
of I solution was used. The iodine was standardized against 
As 2 0 3 dissolved in HC 1 by the reaction AsC1 3 + 2 HC 1 -|- 2 1= 
AsC1 5 -f- 2HI. Twenty-five hundredths gram of As 2 O a required 
49.25 cc. of I solution. 

What is the percentage of S in the sample? 


Grams of sample 

Grams of S 

Cc. I solution 

Grams of As 2 08 

95 

(0.000576) 

( 0 - 35 ) 




49-25 

O.25 


"64.14”_ 


“197.92” 


(0.001645) 

1 

(0.005076) 

100 

(0.000606) 




The calculation may be made by logarithms as follows: 


X 

O.25 

9-39794 - 10 

X 

I.OO 

0 

— —- 

49-25 

8.30759 - 10 

X 

64.14 

1.80713 

-T- 

197.92 

7.70351 -10 

X 

0-35 

9.54407 —10 

-f- 

1.00 

0 

X 

100.00 

2 

-r- 

95.00 

8.02228 -10 



6.78252 — 10 — 0.000606 = Per cent. 


Example 5 .—Given the following data, calculate the percen¬ 
tage of Fe in a sample of crude ferric chloride weighing 1 gram. 
The I liberated by the reaction 2 FeCl 3 + 2 HI = 2 HC 1 + 


















38 


NOTES ON CHEMICAL ANALYSIS 


2 FeCl 2 -f- I 2 is reduced by the addition of 50 cc. of Na 2 S 2 0 3 
solution and the excess titrated with standard I solution, and 
requires 7.85 cc. 45 cc. of I solution = 45-95 cc - Na 2 S 2 0 3 
solution. 45 cc. of As 2 O a solution = 45- 2 7 cc - of 1 solution. 
1 cc. of As 2 0 3 solution = 0.005160 gram of As 2 0 3 . 


Grams of 
sample 

Grams of 

Fe 

Cc. of I 
solution 

Cc. of 
Na 2 S 2 0 3 so 

Grams of 
As 2 0 3 so 

Grams of 
ASjOj, 




50.00 





7-85 

(8.02) 



I 

( ) 


(41.98) 




( ) 

45.00 

45-95 




( ) 

45-27 


45-00 



( ) 



1.00 

0.005160 


“ 55-84 




49 . 48 ” 

loo 

( 23 . 79 ) 






In solving this problem the first step is to find the thiosulfate 
value of the iodine used in titrating back, and then by subtrac¬ 
tion find the amount of thiosulfate reacting with iron. By keep¬ 
ing in mind the order of operations, problems of this sort can be 
tabulated completely before beginning the calculation. After 
completing the subtraction, the other rectangles can be stepped 
off to the final logarithm without solving for the intermediate 
numbers. 

The calculation is as follows: 


x 7.8s 0.8949 


X 

0.00516 

7.7126 -10 

x 45.95 1.6623 


X 

55-84 

1.7469 

-7- 45-00 8.3468 

—10 

X 

49.48 

45.00 

8.3056 -10 
1-6532 

0.9040 

= 8.017 

X 

1.00 

45.00 

45-27 

0.0000 

1.6432 

8.3442 - to 

50.00 


X 

41.98 

1.6230 

8.02 


X 

45-95 

100.00 

8-3377 - 10 
2.0000 

41.98 



1.00 

0.0000 

1.3764 = 23.79 

















































TABULATION METHOD FOR DIRECT RATIOS 


39 


Example 6.—A mixture of pure chlorides of sodium and 
potassium from 0.5 gram of feldspar weighs 0.1500 gram, and 
after solution in water requires 22.71 cc. of 0.1012 N silver ni¬ 
trate for the precipitation of the chloride ions. What are the 
percentages of Na 2 0 and K 2 0 in the sample? 


Grams of 
sample 

Grams of 
NaCl 

Grams of 
Na s O 

Grams of 
KC 1 

Grams of 

k 2 o 

Cc. of 
AgN 0 3 

Cc. normal 






“1 

0.10x2” 

Q -5 





22.71 

(2.2983) 


(x=o.o 7756 ) 

(0.04113) 




(y = 1.3267) 




(0.1500 — x) 
(= 0.07244) 

(0.04576) 


(2.5983-y) 

(= 0.9714) 


“0.05846 

“0.0310 

“0.07456 

“0.04710 


1” 

100 


(8.23) 


( 9 - 15 ) 




This problem is solved by algebra, or it may be visualized 
geometrically by taking advantage of the fact that the unknown 
quantities are in proportion with 1 cc. normal, so that in each 
case one unknown is the numerical product of two other num¬ 
bers. As a product may be represented by the area of a rectangle 
of which the factors are the sides, the solution is as follows. 


H 


s 


0 


d 


G 


X 

.1500—x 

NaCl 

K.C1 


D 


2.2983 


Representing the value of 1 cc. normal in grams of the two 
chlorides as ordinates and the number of cc. as the abscissa, 
the area ACEFGH .= 0.1500, the combined weight of the chlor¬ 
ides. From these figures we can obtain the area ACDH, and 
































40 


NOTES ON CHEMICAL ANALYSIS 


by subtraction GDEF — 0.01564. Dividing this by 0.0161 we 
obtain 0.9714, the number of cc. N consumed by KC 1 , and by 
subtraction 1.3269 cc. consumed by NaCl, and so on. 

This method leads to a formula for averaging the results of 
an assay made on two portions of a sample separately. When 
one of the portions is very small and of high assay, as in the 
case of metallics in an ore, it is convenient to reduce the assay 
of the metallics to a correction to be added to the assay of the 
fine. The correction being small the calculation is less laborious. 

The proportions of fine and metallics being recorded in per¬ 
centage, the abscissa becomes 100, and the two ordinates the 
assays of the fine and metallics, either in percentage or ounces 
per ton. The area of the rectangle above the dotted line, GDEF, 
is exchanged for one of length 100, the height of which is the 
correction to be added. 

Multiply the difference between the two assays by the per¬ 
centage of the portion having the higher assay, divide by 100, 
and add the quotient to the lower assay. 


CHAPTER III 


SOME PROPERTIES OF THE COMMONER ELEMENTS 

Hydrogen.—H, heads the list in the periodic system with but 
slight tendencies toward either acid or alkaline properties, being 
midway in the electro-potential series. It forms the positive ion 
in all acids, and is included in the negative ion of the weakest 
of acids, HOH. 

H is of one valence, i. 

H is ordinarily weighed as water, by absorption in H 2 -S 0 4 or 
CaCl 2 . 

Oxygen.—O, like H, has no decided acid or alkaline properties 
of its own, though in combination it is generally found in the 
negative ion. 

Its valence is constant, 2. 

It is weighed generally as H 2 0 . 

Nitrogen.—N heads the fifth group, of generally acid tenden¬ 
cies, though forming part of the positive ion NH 4 . 

The commoner valences of N are 3 and 5, being more stable 
in the latter condition. By the action of metals HNO s is re¬ 
duced to NO, but its reduction is not the basis of titration. 

It forms no weighable insoluble compounds, and in all of its 
forms it is volatile at temperatures below redness. 

It is determined by reduction to NH 4 OH in alkaline solution 
by the action of metals, distilled and titrated as an alkali. 

Carbon.—C inclines slightly to the acid side in its commonest 
form, CO E . Electrolytically it is negligible. 

With the one exception of CO, its valence is 4, and its reduc¬ 
tion is not an analytical procedure. 

It is insoluble as C, and is weighed as such when so found in 
the sample. In analysis it is weighed as C 0 2 by absorption in 
alkalies, or as BaC 0 3 . 

Boron.—B is notable for being in most forms involatile, yet 
being assayed by distillation. 

B has a valence of 3, and is not reduced under laboratory 
conditions. Its common compounds are the borates, compounds 
of the oxyacid B(OH) 3 , such as NaB 0 2 and Na 2 B^O T . 


42 


NOTES ON CHEMICAL ANALYSIS 


B forms no weighable precipitates. It is distilled as methyl 
borate B(OCH 3 ) 3 , and the distillate may be weighed. This 
vapor gives a green flame color. 

B(OH) 3 bleaches phenolphthalein but does not redden methyl 
orange. Titration methods are based on this difference from 
other acids, C 0 2 being easily expelled. 

Silicon.—Si succeeds C in Group IV of the periodic system, 
with decidedly acid properties. 

It has a practically constant valence of 4, and its reduction to 
Si is a matter of great difficulty. 

It is weighed as Si 0 2 . 

SiF 4 is gaseous. In the presence of chlorides, Si is slightly 
volatile at high temperatures by the formation of SiCl 4 , so that 
thorough washing of Si 0 2 is necessary, with careful roasting be¬ 
fore ignition. 

H 4 Si 0 4 , when produced in solution by adding acid to silicates, 
will remain completely in solution in a concentration as great 
as 1 per cent, but by evaporation or the use of coagulants gela¬ 
tinous H 2 SiO s is partly precipitated, which cannot be filtered, as 
it clogs the filter. Si 0 2 must either be kept in solution or else 
made insoluble by drying. Perfect precipitation is a matter of 
the greatest difficulty, as too high a temperature causes the re¬ 
formation of soluble silicates. A practical limit of drying tem¬ 
perature is 130°. 

Sulfur.—S follows O in the series, having in common with it 
the ability to form electro-negative ions with other elements, as 
in the case of HSH. With O it forms strong acids. 

Its valences are 2, 4 and 6, the strength of the acids formed 
increasing with the valence. 

H 2 S is decomposed by free I, with the formation of free S 
and HI. Both H 2 S and H 2 S 0 3 are oxidized to H 2 S 0 3 by KMn 0 4 . 
These reactions are used for titration. 

Hexavalent and tetravalent S are reduced to divalence by H 
at red heat. Elemental S and the lower valences are oxidized to 
hexavalence by Br, and by O in the presence of catalysers. Diva¬ 
lent and tetravalent S are oxidized to hexavalence by a mixture 
of three parts HNO s and one part HC 1 . 


SOME PROPERTIES OP THE COMMONER ELEMENTS 


43 


BaS 0 4 is the compound most commonly weighed. 

Only the sulfates of the stronger bases are involatile on igni¬ 
tion in air, but sulfides of these bases are partly converted to 
sulfates on ignition. 

Phosphorus.—Following N in the series, P is more decidedly 
acid in its tendencies though its acidity is not so powerful. Phos- 
phonium, the homolog of ammonium, is too unstable to be of 
analytical importance. 

The valences are 3 and 5. The trivalent forms are unstable, 
and are not used in the assay of P, though hypophosphorous 
acid HPH 2 0 2 is a valuable reducing agent. 

For purposes of its assay, P is oxidized to the pentavalent 
form, if not so already, KMn 0 4 being a convenient reagent for 
that purpose, in acid solution. 

P is separated as MgNH 4 P 0 4 - 6 H 2 0 and weighed as Mg 2 P 2 0 7 . 
It is also weighed as the “yellow precipitate,” ammonium phos- 
pho-molybdate, (NH 4 ) 3 P 0 4 -i 2 MoO s - 3 H 2 0 , and weighed as 
such or titrated, either by alkali or by reducing the Mo. 

Phosphine is the only volatile compound of importance, and 
its formation is prevented by avoiding the evolution of H during 
the decomposition of the sample. 

Phosphates are occluded in and also absorbed by metastannic 
acid, and are occluded in hydrates, particularly those of Fe and 
Al. This property is used for the concentration of P in the 
sample, by the separation of elements not included in those 
precipitates. 

Tungsten.—Coming near the bottom of the series, the properties 
of the series are so weakened in W that it is known more by its 
individual peculiarities. 

Its valences are 2, 4, 5 and 6, of which the last is the most 
stable. In its divalent and tetravalent forms it is a weak base, 
unstable, and neither valence is formed in analysis. 

In HC 1 solution Zn reduces W to blue WC 1 5 , unstable, but 
used as a test. 

With O hexavalent W forms the stable W 0 3 and the acid 

h 2 wo 4 . 

Oxidation and reduction are not used in its assay. 


44 


NOTES ON CHEMICAL ANALYSIS 


Like silica, the acid is soluble, unless dehydrated. Its most in¬ 
soluble compound is precipitated from acid solution by cinchon¬ 
ine hydrochloride. It is weighed as W 0 3 ; color, yellow. 

The sulfide is formed only by the acidulation of the alkaline 
sulfide solution. Tartaric acid prevents its formation. 

Tungstates are soluble in alkalies, and are not occluded in 
hydrate precipitates. 

W is not volatile from solution, nor on ignition, but may be 
volatilized by heating the oxide in CC 1 4 , forming WC 1 6 . 

Fluorine.—This is the lightest of the halogens, and decidedly 
different from the others. Its valence is i, and it is not reducible 
by analytical methods. 

Its characteristic compound is HF, a moderately strong acid 
and a powerful solvent. 

F is precipitated and weighed as CaF 2 , which is slightly soluble 
in water. 

SiF 4 is a gas, and by means of it F may be determined by 
difference, or by distillation. 

Chlorine.—The valences of Cl are i, 5 and 7, all of which are 
stable, and some unstable compounds which suggest other val¬ 
ences between 1 and 5. The higher valences are not produced 
as an analytical procedure, differential reduction being used in 
the determination of the various ions. 

HC 1 is typical of the monovalent form; a strong acid and a 
solvent. 

Free Cl, since it has oxidizing power, is brought to mono¬ 
valence by reducing action, all reducing agents reacting with it. 

Chlorates, from HC 10 3 , the pentavalent form, are reduced by 
ferrous salts and H 2 SO ;{ , which do not reduce perchlorates. 

Perchlorates, from PIC 10 4 , are reduced in acid solution by 
metallic Zn, which also reduces chlorates. 

AgCl is insoluble in dilute acids, and soluble in NH 4 OH or 
Na 2 S 2 0 3 solution. Cl is precipitated as AgCl and weighed as 
such or as Ag. AgCl is involatile on heating to fusion. 

Bromine.—Br has the same valences as Cl, and forms homo¬ 
logous compounds, but its affinities are lower and it is easily dis¬ 
placed from its compounds by Cl. 


some: properties op the commoner ELEMENTS 


45 


As it is precipitated as AgBr and can be weighed both as 
such and as Ag, Cl and Br may be determined together by cal¬ 
culation. 

Iodine.—I follows Br in the series, with higher boiling points, 
and weaker affinities. 

Hydriodic acid, HI, is oxidized to inrolatile iodic acid, HIO s , 
by Cr 0 3 , while hydrochloric and hydrobromic acid are oxidized 
to gaseous Cl and Br. This permits the differential determina¬ 
tion of all three halogens together. 

Arsenic.—This element, the most electro-negative of those 
classed as metals and found in alloys, carries to extremes many 
properties which it shares with other metals. Its acid properties 
are most pronounced, its compounds are with the exception of 
Hg the most volatile, its sulfides are least soluble in acids and 
most soluble in alkalies, and it has the least tendency to electro¬ 
deposition. 

Its valences are 3 and 5. Both conditions are stable on ex¬ 
posure to air. In hot concentrated HC 1 , AsC 1 5 is readily re¬ 
duced to AsC 1 3 by the presence of ferrous salts, and in concen¬ 
trated and more dilute acid by cuprous salts, H 3 P 0 2 and H 2 S 0 3 . 
Organic matter in fuming H 2 S 0 4 also reduces pentavalent As. 

Arsenic solutions in presence of acid are reduced by iodides, 
setting free I. 

Arsenious compounds are oxidized by HN 0 3 , by free Cl and 
by free I in neutral solution, but the last has but slight effect 
in acid solution. 

As is precipitated and weighed as As 2 S 3 . It is also precipi¬ 
tated as MgNH 4 As 0 4 and weighed as Mg 2 As 2 0 7 . 

AsC 1 3 is volatile with boiling HC 1 , 50 per cent or stronger. 

AsH 3 , gaseous, is formed by nascent H on the solution of 
metals in acid, in presence of As in any soluble form. 

All compounds of As with volatile elements are volatile on 

ignition. 

As is readily precipitated as As 2 S 3 from its trivalent salts in 
acid of any strength. Its color is canary yellow. It is easily 
soluble in all alkalies, even (NH 4 ) 2 C 0 3 , which last serves to 
separate it from other members of its group. 

4 


46 


NOTES ON CHEMICAL ANALYSIS 


As 2 S 5 is slowly precipitated, mixed with As 2 S 3 , from penta- 
valent solutions in dilute acids. From HC1 equal to 75 per cent 
or more of its ordinary reagent strength, 1.19 specific gravity., 
As 2 S 6 is completely precipitated, making a separation from all 
other basic ions except Se. Precipitated As 2 S 5 has the same 
properties as As 2 S 3 except weight. 

As is precipitated by ammonium molybdate. 

When alloys containing As with Sn or Sb are decomposed with 
HN0 3 , the insoluble residue contains all or part of the As. 

Fe(OH ) 3 and several other hydrates, if formed in presence 
of arsenic solution, will carry all or part of it into insoluble 
precipitate. 

Antimony.—The properties of Sb are similar to its serial an¬ 
tecedent As, modified in the direction of the electro-positive pole. 
It has also much in common with its neighbor Sn. 

Its valences are 3 and 5 . Like Sn, it forms an apparently te- 
travalent oxide, which may be a combination of its regular 
valences. 

Trivalent Sb acts as a base. Sb 2 0 3 - reacts with strong bases 
to form antimonites, such as NaSb0 2 . 

Pentavalent Sb acts as a base. Sb 2 0 5 has decidedly acid prop¬ 
erties, as HSb0 3 and H 4 Sb 2 0 7 . 

SbCl 5 is reduced to SbCl 3 by ferrous salts in strong HC1, and 
in strong or weak acids by cuprous salts, H 3 P0 2 and by HaSO*. 
The last acts best in warm solutions, on account of its volatility. 

Antimonic solutions in presence of acid are reduced by iodides, 
setting free I. 

Antimonious compounds are oxidized by HNO a , by free Cl 
and by free I in neutral solution. 

Small quantities of Sb are precipitated as Sb 2 S 3 , and weighed 
as Sb 2 0 4 . It is also precipitated and weighed as Na 2 H 2 Sb 2 0 7 . 

SbCl 3 is volatile with HC1 at a temperature approaching that 
of fuming H 2 S0 4 . 

SbH 3 , gaseous, is formed by the action of nascent H on solu¬ 
tions of Sb. As metallic Sb is insoluble in HC1, and is repre¬ 
cipitated during solution of alloys in that acid, the danger of 
loss as SbH 3 is slight. 


SOME PROPERTIES OP THE COMMONER ELEMENTS 


47 


Antimonious compounds are volatile at ignition temperatures. 
By thorough oxidation Sb 2 0 4 is produced, which may be ignited 
without loss. 

Sb 2 S 3 and Sb 2 S 5 are so nearly alike in all their properties 
as to be indistinguishable. Their color is red with a slight tinge 
of yellow. They are precipitated in HC1 of all concentrations 
up to 30 per cent of the reagent, cold or 16 per cent hot, but in 
the higher concentrations are unstable on exposure to air. They 
are soluble in hydrates and sulfides of Na and K, and in sul¬ 
fides of NH 4 . 

Sb salts in solution are easily hydrolyzed, considerable excess 
of acid being necessary to keep them in solution. Tartaric acid 
prevents hydrolysis, and permits the formation of neutral and 
alkaline solutions. In this respect Sb resembles its serial suc- 
cedent, Bi. 

Though the hydrates are soluble in excess of alkali, they 
are made insoluble by occlusion in other hydrates, such as 
Fe(OH)* 

PbS0 4 will occlude some Sb if the latter is present in more 
than traces in the H 2 S0 4 solution. 

Tin.—Sn resembles analytically none of the common elements 
in its series, but has much in common with its lateral neighbor 
Sb. 

Pb, Ni and Fe, though electro-positive to Sn, are unable to 
precipitate it electrolytically, Zn being the first metal having 
that property. 

The valences of Sn are 2 and 4 . 

Divalent Sn acts as a base and its oxide forms stannites such 
as Na 2 Sn0 2 in excess of alkali. 

Tetravalent Sn acts as a base. Its oxide forms stannic acid, 
H 2 Sn0 3 and metastannic acid, H 10 Sn 5 O 15 . 

SnCl 4 is reduced to SnCl 2 in HC1 by the solution of metallic 
Pb, Fe or Ni. Free I oxidizes stannous solutions to stannic. 

Sn is converted to metastannic acid by action of HNO s on 
the metal, and is precipitated quantitatively as SnS 2 . Both are 
weighed as Sn0 2 . 


48 


NOTES ON CHEMICAL ANALYSIS 


SnCl 4 in absence of H 2 0 is highly volatile, and its volatility 
is considerable on the evaporation of chloride solutions nearly 
or quite to dryness on the waterbath, or on the evaporation of 
mixed HC1 and H 2 S0 4 solutions to the expulsion of H 2 0. Pro¬ 
longed boiling in concentrated HC1 entails some loss, but this is 
negligible in analytical work unless the solution boils almost dry. 

Sn compounds may be partly volatilized by the reducing action 
of C if ignited with insufficient air. 

SnS 2 may be completely precipitated from HC1 solutions as 
strong as 16 per cent cold or 8 per cent hot. The presence of 
H 2 C 2 0 4 prevents its precipitation, but not that of SnS. 

SnS 2 is readily soluble in hydrates and sulfides of Na and K, 
and in sulfides of NH 4 . SnS is not soluble, except by oxidation. 

SnS 2 is brownish yellow when collected, though it may be 
white when first precipitated from HC 2 H 3 0 2 . SnS is greenish 
brown, and more dense than SnS 2 , which is slimy. 

Sn salts have a marked tendency to hydrolysis. Its hydrates 
are too slimy to filter alone. 

Occluded with other hydrates, Sn may be precipitated and 
filtered. 

Sn has no tendency to combination with PbS0 4 , as is the case 
with Sb. 

Selenium.—Se follows S in the series, and its compounds are 
similar, but its properties incline more to those of a metal. It is 
strongly electro-negative, and easily reduced electrolytically. 

Its valences are 2 , 4 and 6 . The higher valence is unstable, 
H 2 Se0 4 being reduced to H 2 SeO a by boiling with HC1. H 2 SO s 
reduces H 2 SeO s to Se. H 2 S produces an unstable sulfide, SeS, 
which reduces quickly, but as the element remains insoluble in 
acid, and dissolves in alkaline polysulfides, Se is included in the 
H 2 S group. 

Se is precipitated and weighed as the element. It may be 
completely reduced and precipitated in HC1 as strong as 80 per 
cent. Seventy per cent is customary, which gives a separation 
from Te. Se is red when precipitated, turning to black on heat¬ 
ing. Metallic Se is volatile on ignition. 


SOME} properties of the commoner elements 49 

The chlorides of Se are more or less volatile, and special 
precautions need to be taken during analysis to prevent loss. 
On this account assays of Se should be made on separate samples. 
Se can be separated by volatilization from elements having in¬ 
volatile chlorides. 

Like its neighbor As, Se is occluded in hydrates when in solu¬ 
tion at the time of precipitation. 

Tellurium.—Te, following Se in the series, resembles it closely 
in all its compounds and reactions. The same reagents oxidize 
and reduce it. 

It is precipitated and weighed as the element. It is more 
soluble than Se, 60 per cent HC1 preventing its precipitation by 
H 2 SO s . From io per cent to 15 per cent is the customary 
strength for precipitation. The precipitated element is black. 

The chlorides of Te are volatile, giving the same uses and 
dangers as those of Se. It follows Se in reactions with H 2 S and 
in occlusion. 

Molybdenum.—With atomic weight between Se and Te, but on 
another branch of the same series, Mo is decidely different from 
them. 

Its valences are 2 , 3 , 4 , 5 and 6 . Hexavalent Mo forms molyb- 
dic acid, H 2 Mo0 4 , and many addition and substitution products 
of M0O3. In the other valences Mo is basic. It is not reduced 
to metal in the wet way, but its reduction by Zn in acid solution 
to the trivalent form, and oxidation to the hexavalent by KMn0 4 , 
is the basis of the best method of assay. By HI it is reduced 
to pentavalence with liberation of I. Mo is not volatile from 
solution, but ignition is difficult. 

H 2 S precipitates insoluble MoS 3 from acid solution, but dur¬ 
ing precipitation reduces a part of the solution below hexavalence 
to a blue solution of unknown valence near 5 , which forms no 
sulfide. The sulfide is soluble in alkaline sulfides, giving a red 
color. 

There are a number of insoluble molybdates, the most con¬ 
venient of which is PbMo0 4 , which is precipitated in HC 2 H 3 Q 2 
solution. The solubility of hexavalent Mo in NH 4 OH and its 


50 


NOTES ON CHEMICAL ANALYSIS 


freedom from occlusion in precipitated hydrates gives the best 
method of separating it from the other members of its group. 

Silver.—Ag is unique among the heavier metals in having no 
higher valence than i. 

It is classed among the noble metals because its most stable 
form is the metallic, most of its compounds being reduced by 
heat alone. From solution it is reduced to metal by such re¬ 
agents as FeS0 4 . 

It is precipitated and weighed as AgCl, and in the fire assay 
as metallic Ag. 

It forms no volatile compounds. 

Ag 2 S is easily precipitated and insoluble in both acids and 
alkalies. 

The solubility of its chloride in NH 4 OH and it insolubility in 
dilute HN 0 3 serve to distinguish it. 

Mercury.—Hg has hardly any resemblance to the other ele¬ 
ments of its series. It has two valences while they have one. Its 
low melting point and the volatility of all its compounds dis¬ 
tinguish it from all others. Electrically it is regular, being next 
to, and negative to H. 

The valences of Hg are 1 and 2. It is stable in both valences, 
though some of its compounds have a tendency to decompose 
and reduce to Hg. Change of valence is used in methods for 
assaying salts of Hg. 

Hg is weighed generally as Hg, though the sulfide HgS may 
be used. All compounds of Hg, without exception are volatile 
at moderate ignition temperatures, but volatility from solution 
is not a source of loss. 

HgS, the only sulfide, is less soluble in acid than any other 
member of its sub-group, and it is insoluble in alkalies except 
where the formation of double sulfides of Na or K is possible. 

HgCl is of interest, as by its precipitation, insoluble in acids, 
and insoluble but turning black by reduction in NH 4 OH, mono¬ 
valent Hg may be identified and separated. 

The reduction of Hg compounds to metal by heating in con¬ 
tact with Fe and its distillation form the basis of most assay 
and metallurgical work with Hg. 


some; properties op the commoner elements 51 

Lead.—In the periodic system Pb is far removed from its an¬ 
alytical associates, except its neighbor Bi. In the Eothar Meyer 
table its characteristics are more clearly indicated. 

Electro-positive to H and several other metals, the character 
of Pb in this respect is masked by the insolubility of its chloride 
and sulfate, and by its ability to precipitate on the anode as Pb 0 2 . 

Pb has only one valence, 2, in solution, but may be tetravalent 
as oxide. Its reduction, as such, to divalence, is easy, inter¬ 
ference coming from the formation of insoluble compounds. 
The tendency of Pb 0 2 to reduce is shown by its ability to oxi¬ 
dize Mn to permanganic acid. Titration methods are based on 
this reduction. 

Pb is not volatile from solution, but Pb and PbO are easily 
volatile on ignition, and other compounds are reduced by heating 
with C, so ignition of precipitates on paper is difficult. 

Pb is precipitated and weighed as PbS 0 4 , PbCr 0 4 and Pb 0 2 . 

PbS is precipitated by H 2 S from acid and alkaline solutions, 
black. The allowable strength of HN 0 3 is 5 per cent. In HC 1 
the acidity should not be more than 4 per cent at 40° or 2 per 
cent at 6o°. Above these limits the reddish brown chlor-sulfide, 
a mixed chloride and sulfide, may be precipitated, with danger 
of incomplete precipitation. On this account PbS from HC 1 
should be washed with solution containing H 2 S. The sulfide is 
insoluble in alkalies and alkaline sulfides. 

The most soluble Pb compound is the acetate, but this re¬ 
quires an excess of HC 2 H 3 0 2 to prevent hydrolysis. 

In accordance with its electrolytic position, Pb is dissolved in 
HC 1 with evolution of H, but heat $nd sufficient dilution are 
necessary to prevent the chloride from occluding and protecting 
the undecomposed metal. The solubility of PbCl 2 in acid solu¬ 
tions at room temperature is, roughly, as follows: 

% HC 1 o 2.5 5 10 15 20 30 100 

% Pb 0.63 0.08 0.05 0.06 0.08 0.09 0.20 15 

PbS 0 4 formed by boiling H 2 S 0 4 solutions to fumes of S 0 3 
will occlude Bi, Sb, Ba and Sr, if those elements are present in 
quantity more than a few milligrams, causing some Pb to re- 


52 


NOTES ON CHEMICAL ANALYSIS 


main insoluble in NH 4 C 2 H 3 0 2 . CaS 0 4 may remain undis 
solved in dilute H 2 S 0 4 , dissolve in the acetate, and be occluded 
in the PbCr 0 4 . Methods of analysis must provide for these 
possibilities. 

The easy fusibility of PbO is a distinguishing characteristic 

of Pb. 

Bismuth.—Bi shows the regular characters of its place in the 
series, which increases in the basic tendency with the atomic 
weight. In the electro-potential series it is positive to Cu and H, 
and next to Cu, to the detriment of the Cu assay. 

Bi has one valence, 3. In the wet way its hydrate is reduced 
to metal by alkaline stannites, such as Na 2 Sn 0 2 . 

Bi is precipitated as carbonate and weighed as oxide. It is 
precipitated and weighed more commonly as BiOCl, formed by 
hydrolysis of the chloride. 

Bi is precipitated from HC 1 , HNO s and H 2 S 0 4 as strong as 
5 per cent by H 2 S. From HC 1 the precipitate is not easily 
washed, tending to run through the filter. 

Bi 2 S 3 is insoluble in alkalies, but is difficult to wash except 
with NH 4 S x . It is precipitated in good form from ammoniacal 
tartrate or cyanide solutions. The tartrate gives a good separa¬ 
tion from Te, and the cyanide from Cu. 

The carbonate is completely precipitated with difficulty from 
(NH 4 ) 2 C 0 3 solution. It is useful as a separation from occluded 
sulfates. 

The oxychloride is precipitated easily by diluting a concen¬ 
trated slightly acid solution of the chloride. It tends to occlude 
Te0 3 and S 0 3 which must be removed before the precipitation. 

The occlusion of Bi by PbS 0 4 has been mentioned. 

Copper.—Being followed in the series by noble metals, Cu tends 
to stability in metallic form. One step more positive than H, Cu 
is the most adaptable to electrodeposition of all the elements. 

Cu has two valences, 1 and 2, of which the divalent form is 
more stable. Reduction is produced by such reagents as H 2 S 0 3 . 
This is useful in separations, and some titration methods are 
based on it. 


SOME properties op the commoner ELEMENTS 


53 


Cu forms many weighable compounds, of which the oxide, 
precipitated as such or formed by the ignition of the sulfide, is 
most commonly used. The electrolytically precipitated metal is 
the best gravimetric form. 

Cu compounds are not volatile from solution, but Cu 2 Cl 2 is 
volatile on ignition; for which reason Cu precipitates containing 
traces of chlorides must be heated slowly and well roasted be¬ 
fore heating to redness. 

CuS is precipitated from acid solutions. The allowable 
strength of HC 1 is 16 per cent hot and 33 per cent cold; H 2 S 0 4 
as much as 15 per cent, and HN 0 4 limited only by the decom¬ 
position of HoS. The sulfide is ordinarily black, but when pre¬ 
cipitated from dilute HNO s it appears brown. 

The sulfide is slightly soluble in alkaline polysulfides, but par¬ 
ticularly so in NH 4 ,S x . 

CuC 1 2 and Cu(N 0 3 ) 2 are highly soluble in their acids, but 
CuS 0 4 is much less so. Ten grams of Cu, dissolved and heated 
with 20 cc. of H 2 S 0 4 to expel other acids, must be diluted to 
135 cc. to prevent crystallization. 

The blue solution produced by dissolving Cu(OH) 2 in excess 
of NH 4 OH is of value as a basis for color comparison. This 
solubility of the hydrate is used to separate Cu from Fe and 
from the many elements which are occluded by Fe(OH) 3 , such 
as As, Sb, Se, Te and Bi. 

Cadmium.—Cadmium belongs to a series of low melting and 
boiling points, culminating with Hg. It closely resembles its 
antecedent Zn, dififering in slight degree in most of its properties. 
It is electro-positive to H, but not so much so as to make deposi¬ 
tion difficult. 

Its valence is 2. It is not reduced to metal in the wet way. 
On ignition with paper it is reduced and may be volatilized unless 
careful roasting is practiced. Like Zn, the metal is much more 
volatile than the oxide. 

The sulfide is the only insoluble compound of importance. It 
can be completely precipitated from H 2 S 0 4 solution as strong 


54 


NOTES ON CHEMICAL ANALYSIS 


as 5 per cent, the presence of (NH 4 ) 2 S 0 4 assisting to bring 
down small amounts. HC 1 or HNO s may also be used if the 
acidity is not too high. 

The sulfide is also produced from NH 4 OH solution, or am- 
moniacal cyanide, and is insoluble in alkalies. Its yellow color 
is characteristic in its analytical position. 

The sulfate can be ignited without loss, by evaporating the 
solution. 

Zn is likely to be occluded in the CdS precipitate, and two or 
more precipitations are necessary to separate large quantities of 
it. 

Aluminium.—Though there are several elements which show 
many of the analytical properties of Al, so that it has no char¬ 
acteristic reactions by ordinary reagents, the other elements are 
either rare or easily separated. 

Complete separation from the other elements and the appear¬ 
ance of its hydrate make the test ordinarily depended upon for 
its identification. 

While appearing generally as a basic ion, Al has marked acid 
tendencies, forming soluble aluminates with alkalies, such as 
NaA 10 2 . Metallic Al dissolves in NaOH or KOH with evolution 
of H. 

Its valence is 3. It is not reduced to metal in the wet way. 

The chloride and other halogen compounds of Al are volatile 
on ignition. For this reason Al should be precipitated from a 
sulfate or nitrate solution preparatory to ignition. 

A 1 2 S 3 is decomposed by water, the hydrate being completely 
precipitated by NH 4 S x ,in the absence of free NH 4 OH. 

The hydrate is precipitated in a neutral solution containing 
some ammonium salts as a coagulant. It is less soluble in a 
slight excess of acid, such as is formed by boiling ammonium 
salts, than in excess NH 4 OH. 

Al is precipitated and weighed as the phosphate, A 1 P 0 4 . It 
is precipitated as the hydrate, Al(OH) 3 and weighed as A 40 s . 
The highest blast temperature is necessary for its complete 
dehydration. 


SOME PROPERTIES OF THE COMMONER ELEMENTS 


55 


Al(OH) 3 occludes P 2 O s when present, forming the phosphate. 

A 1 forms no colored compounds with ordinry reagents in the 
wet way. 

Chromium.—Cr resembles Mo, its succedent in the periodic 
series, in having a variety of colored precipitates and solutions, 
but has not the same multiplicity of valences. 

Cr has two stable valences, 3 and 6. Trivalent Cr has the 
same behavior as Al, forming hydrates in neutral solutions, sol¬ 
uble chromites with excess of alkalies, and acting as a basic ion 
in acid solutions. 

Hexavalent Cr forms the acids H 2 Cr 0 4 and H 2 Cr 2 0 7 , which 
exist only in solution, forming stable salts. Cr is reduced to 
trivalence by boiling in HC 1 , a property which it shares with its 
succedents Se and Te and its neighbor V. Hexavalent Cr is also 
reduced in acid solution by peroxides, through the formation of 
unstable perchromates, which decompose to the trivalent chromic 
compounds. 

In the acid solution Cr is not easily oxidized to hexavalence, 
KMn 0 4 having no effect, though strong aqua regia does it par¬ 
tially, but in alkaline solution peroxides make the change com¬ 
pletely. 

The reduction of Cr from hexavalence to trivalence is the 
basis of accurate titration methods. 

Cr is weighed as PbCr 0 4 and as Cr 2 0 3 . 

Chromates and vanadates interfere through the similarity of 
their properties. 

Uranium.—U has marked resemblances to its antecedent Cr, 
showing several valences, colored solutions and salts, and both 
acid and basic properties. 

U has one stable valence, 6. In this valence it forms basic 
compounds containing U 0 2 , called uranyl, which was once 
thought to be the element. In reduction reactions a uranyl salt, 
such as U0 2 S0 4 , behaves in the same way that U(S 0 3 ,) 3 would. 

Tetravalent U in solution is sufficiently stable for titration 
purposes. Trivalent U is extremely unstable, being rapidly oxi¬ 
dized to tetravalence on exposure in solution to air. Zinc in 
acid reduces U partly to tetravalence and partly to trivalence. 


56 


NOTES ON CHEMICAL ANALYSIS 


Hexavalent U salts and solutions are yellow. Trivalent U 
solutions are olive green, and tetravalent solutions grass green. 
U is oxidized to hexavalence in acid solution by KMn 0 4 . Ti¬ 
tration methods are used. 

There are no troublesome volatile U compounds. 

UOoS is precipitated completely by NH 4 SH. It is soluble in 
acids. 

NH 4 OH precipitates (NH 4 ) 2 U 2 0 7 , which is ignited and 
weighed as U 3 O g . 

In presence of phosphates or vanadates U 0 2 HP 0 4 or U 0 2 - 
(V 0 4 ) 2 are precipitated on neutralization, instead of the uranate. 
The presence of an excess of phosphates will prevent the forma¬ 
tion of the vanadate. 

Alkaline carbonates produce soluble U compounds, permitting 
easy separations from Fe and Al. 

The reddish brown color produced by K4,Fe(CN) 6 with U 
salts provides a good qualitative test for U, as well as a valuable 
indicator for the titration of Zn. 

Vanadium.—V has some resemblance to its neighbor Cr, but is 
otherwise unique. 

It has one stable valence, 5, with yellow or colorless solu¬ 
tions, and one slightly less so, with blue solutions. An unstable 
pervanadic acid produced by H 2 0 2 is intense red, giving a char¬ 
acteristic test for V. 

Hexavalent V is reduced to tetravalence by H 2 S, H 2 S 0 3 , by 
heating with HC 1 and by electrolysis. Zn reduces it below te¬ 
travalence, and with care the trivalent condition can be com¬ 
pletely produced. KMn 0 4 oxidizes it to pentavalence. Several 
titration methods are used, with KMn 0 4 . 

Pentavalent V with O forms vanadic acid, giving such salts 
as PbV 0 4 . It is soluble in alkalies, but forms several insoluble 
salts, particularly with Pb and Hg. 

Tetravalent V forms basic salts with O called vanadyl salts, 
of which V 2 0 2 C 1 4 is a type. 

V is precipitated as Hg 2 V 0 4 and weighed as V 2 O s , but titra¬ 
tion methods are generally relied on. 


SOME properties op the commoner elements 57 

The occlusion of V with (NH t ) 2 U 2 0 7 is important in analysis. 
It is also occluded partially in Fe(OH) 3 . 

Iron.—Classed in the triads, Fe has but slight resemblance to 
its mates. Standing between Ni and Zn in the electro-potential 
series, it displaces H from acids, and is reduced to metal electro- 
lytically. 

Fe has two valences, 2 and 3, both of which are basic in 
character. 

Trivalent Fe is reduced by H* 2 S and by H 2 SO s , but not by 
HC 1 . Divalent Fe is oxidized by KMn 0 4 but not by I. Titra¬ 
tion is the most accurate method of assaying Fe. 

Black FeS is precipitated by alkaline sulfides from both fer¬ 
rous and ferric solutions. It is soluble in 10 per cent H 2 S 0 4 . 

Fe(OH) 3 is precipitated completely by excess of NH 4 OH, 
and is weighed as Fe 2 0 3 . 

FeCl 3 is volatile at temperatures slightly above boiling, such as 
are obtained by baking an insoluble residue. Excess H 2 S 0 4 
prevents this loss. Precipitates should not be made from the 
chloride solution for ignition. 

P and V, which remain in the filtrate from the H 2 S group, 
are occluded in Fe(OH) 3 , P completely and V partially. 

KCNS is useful to show whether a solution which is being 
reduced still contains any trivalent Fe, and K 3 Fe(CN) 6 to show 
whether any divalent Fe is present, but neither is useful in the 
course of analysis to show whether Fe is present. Many solid 
reagents contain traces of Fe, and H 2 S, unless carefully washed, 
carries it in the spray from the generator. By the time Fe has 
been reached in the analysis, therefore, a trace has generally 
been introduced, and only quantitative comparison with a blank 
determination is a reliable test for small amounts of Fe. The 
color tests are valuable only when they can be used on the sample 
without preliminary separations. 

Titanium.—Ti is without close resemblance among the com¬ 
moner elements, its succedents being rare. Ti itself is far from 
rare, being found in traces in most rocks. 

Its valences are 3 and 4, of which the latter is stable,, and the 
former highly unstable. Tetravalent Ti is reduced by Zn in 


5« 


NOTES ON CHEMICAL ANALYSIS 


acid solution, but must be protected from air to prevent rapid 
oxidation. It is not reduced by H 2 S 0 3 or H 2 S. Trivalent Ti 
solution is violet in color. Tetravalent Ti is colorless. In acid 
solution, H 2 0 2 produces a higher valence with an intense orange 
red color, showing yellow when dilute. This reaction is pre¬ 
vented by the presence of HF. 

In ordinary analysis, Ti remains with Fe, except that in pres¬ 
ence of P 2 0 5 it forms a residue insoluble in acid, which is de¬ 
composed by fusion with Na/X> 3 , and filtering the alkaline solu¬ 
tion. 

When Fe is reduced in the ordinary way, Ti in small quan¬ 
tities does not interfere. After titrating the Fe with KMn 0 4 , 
Ti up to 0.005 gram is estimated by color comparison with H 2 C) 2 , 
and counted as TiO z among the combined oxides from the igni¬ 
tion of the NH 4 OH precipitate. 

Manganese.—Mn is an element of many colors and valences, 
like its neighbors of Group 6 in the periodic system. Its suc- 
cedents in its own series are missing. 

Mn has three valences of interest in analysis, 2, 4 and 7. It 
is stable in all three forms. 

Manganous salts, such as MnS 0 4 , are slightly pink. 

Mn 0 2 is almost black. 

Permanganates, such as KMn 0 4 , are deep purple, showing red 
when dilute. 

Reducing agents in acid solution such as FeS 0 4 , H 2 C 2 0 4 , 
H 2 0 2 and HC 1 reduce both the higher forms to divalence. MnO z 
is formed by the oxidation of manganous salts, as a precipitate. 
In neutral solution, heptavalent and divalent Mn combine to 
form Mn 0 2 . Accurate titration methods are based on these re¬ 
actions. 

Mn is precipitated as NH 4 MnP 0 4 .H 2 0 and weighed as 
Mn 2 P 2 0 7 . 

Volatility is not a source of loss in the Mn assay. 

MnS is precipitated in alkaline solution. A bare trace of 
acid will dissolve it. 

A precipitate approaching MnO a in composition is produced 
by several oxidizing agents, particularly (NH 4 ) 2 S 2 O g , in excess 


SOME PROPERTIES OP THE COMMONER ELEMENTS 


59 


of NH 4 OH, which makes a good separation for small quantities. 
It is ignited and weighed as Mn 3 C 4 . 

Zinc.—Zn and Cd, its succedent in the series, are much alike, 
differing principally in the color and solubility of their com¬ 
pounds. 

Zn is the most positive of the metals which can be electro- 
deposited under laboratory conditions, its properties approaching 
those of an alkali though it forms soluble zincates in excess of 
KOH or NaOH, metallic Zn dissolving with evolution of H. 

Its valence is 2. It is not reduced by reagents. 

It is one of the most volatile of the metals, but its oxide and 
all other compounds except the halides are involatile on ignition. 

Zn is precipitated as ZnS and weighed as ZnO. With the 
utmost precautions, some S is likely to remain as ZnS 0 4 . 

ZnS is the only white sulfide of the common elements. It is 
precipitable in a higher acidity than others of the ammonium 
sulfide group, as much as 0.1 normal H 2 S 0 4 , or 0.2 per cent of 
the reagent, including the acid combined with the Zn, being 
permissible. 1 

Zn is also precipitated completely in solutions containing sul¬ 
fates with not more than 0.1 per cent excess of HC 1 , and in 
HC 2 H 3 0 2 as strong as 10 per cent. These acid precipitations 
are useful as separations from Ni and Co. 

Nickel and Cobalt.—Ni and Co resemble Cu so closely in many 
respects that it would seem that they should occupy the vacant 
space in the zero group. 

Many of their reactions are identical, and will be described 
together. 

Electrolytically they are negative to Fe and Zn, and are easily 
deposited from alkaline solutions. 

Both are divalent in solution, and decidedly basic in their ten¬ 
dencies. 

Ni solutions are green in acid and blue in excess of NH 4 OH, 
while Co forms rose pink solutions. When both are present, the 
colors may neutralize each other, giving an almost colorless 
solution. 

*G. Weiss. Cf Scott; “Standard Methods of Chemical Analysis.” 


6o 


NOTES ON CHEMICAL ANALYSIS 


Volatile compounds give no trouble. 

Both are electrodeposited and weighed as metal, or as sul¬ 
fide and weighed as oxide. 

Their sulfides are peculiar in that a slight excess of mineral 
acid will prevent their precipitation, but the precipitate is very 
slightly soluble in acids, except by decomposition of the sulfide. 
The sulfides are black, and are precipitated from NH 4 OH solu¬ 
tion and coagulated by adding a slight excess of HC 2 H 3 0 2 after 
precipitation, for better filtration. 

Ni is precipitated with di-methyl glyoxime and weighed as 
NiC 8 H 14 N 4 0 4 , this being a separation from Co and Zn. 

Co is precipitated by nitroso-beta-naphthol, ignited and weighed 
as Co 3 0 4 . This is a separation from Ni and several other ele¬ 
ments. 

Calcium.—Ca is one of the strongest bases, almost equal to the 
alkalies, its alkalinity being reduced by the slight solubility of 
its oxide. 

Its valence is 2. It is not reduced to metal under laboratory 
conditions. 

Its halides are volatile on ignition, but in combination with O 
it is highly involatile. 

Its sulfide is soluble in water. Alkaline sulfides are there¬ 
fore better media than ammonia for separating Ca from the 
ammonium sulfide group. 

Ca is ordinarily precipitated as CaC 2 0 4 .H 2 0 and weighed as 
CaO, or the oxalate titrated with KMn0 4 . 

The oxalate precipitate tends to occlude Mg. 

Magnesium.—Mg is almost as strong a base as Ca, but its ox¬ 
ide is almost insoluble in water, giving it slight alkaline proper¬ 
ties. 

Its valence is 2 , and it is not reducible. 

Its salts are generally more soluble than those of Ca. As both 
are separated together from most other bases, only the separa¬ 
tion of Mg from Ca need be considered. 

None of its compounds are volatile. 

Mg is precipitated as MgNH 4 P0 4 6 H 2 0 and weighed as 
Mg 2 P 2 0,. 


some: properties op the: commoner elements 6i 

Barium.—Ba is a base and an alkali of about the same strength 
as Ca. 

Its valence is 2 , and it is not reducible. 

Its solubility during separations is about the same as that of 
Ca, except that the sulfate and the carbonate are insoluble. 
Since H 2 S always produces some H i2 S0 4 , BaS0 4 will separate 
all through the analysis, if it is not separated at the start. As 
it rarely occurs in alloys, and generally as the sulfate in minerals, 
it is generally found in the residue after the expulsion of SiF 4 . 

Ba is precipitated and weighed as BaS0 4 . BaS0 4 is decom¬ 
posed by fusion with Na 2 C0 3 , BaCO s being insoluble in water. 

Strontium.—Sr has most of the general characteristics of Ca 
and Ba, standing between the two as to the solubility of the sul¬ 
fate. In the absence of Ba, Sr will be found in the oxalate pre¬ 
cipitate with Ca. Special methods are used for their separation. 

Potassium.—K has a valence of i, is not reduced to metal by 
laboratory methods, and is not separated in the regular course 
of analysis. 

Special methods are used to separate other elements except 
the other alkalies, after which K is precipitated and weighed as 
chloroplatinate, K 2 PtCl 6 , or perchlorate, KC10 4 . 

The purple flame color of K is distinctive. 

All the compounds of K are soluble in water, even those used 
for its assay, which are separated from the corresponding com¬ 
pounds of Na by dissolving the latter in alcohol. 

Sodium.—Na is similar to K, except that the chloroplatinate 
and the perchlorate are soluble in both water and alcohol, but 
the pyroantimonate, Na 2 H 2 Sb 2 0 7 .H 2 0 is very slightly soluble 
in water and insoluble in a mixture of half water and half al¬ 
cohol. 

The flame test for Na, an intense yellow, is too delicate to be 
useful, since almost every substance will give the test. It may 
be used, however, to identify a sodium compound if a minute 
portion is dissolved in pure water and a drop gives a strong color. 

Sodium is ordinarily weighed as chloride, any K or Li being 
afterward determined and subtracted. 


5 


62 


NOTES ON CHEMICAL ANALYSIS 


Lithium.—Li is distinguished principally from the other al¬ 
kalies by its intense carmine red flame color. Its chloride is 
soluble in amyl alcohol, while the chlorides of Na and K are not. 
The Gooch separation is based on this. 2 


2 Scott, “Standard Methods of Chemical Analysis.” 


CHAPTER IV 


REAGENTS 

Ammonia Water.—The ordinary soluiton has a specific gravity 
of 0.9 containing 28.5 per cent of NH 3 , which makes it about 15 
normal. Owing to its volatility, the bottle on the shelf may be 
10 per cent weaker. 

NH 4 OH is a much weaker base than NaOH or KOH. Am¬ 
monium salts lose NH 3 on boiling and cause the solution to be¬ 
come acid. 

They may be removed from a solution without evaporation 
and ignition by warming with alternate additions of HN0 3 , 
and HC1, which decomposes NH 4 OH to N and H 2 0. 

Ammonium salts are the best coagulants for precipitates, since 
they are easily soluble in both acid and alkaline solutions and 
cause less trouble from precipitation than do the fixed alkalies. 
The convenience of having an alkali supplied in liquid form, 
from which salts can be made by adding acid, gives ammonia 
the preference over the fixed alkalies in most analytical oper¬ 
ations. It is often of advantage to be able to boil off the excess 
of alkali, which can be done only with ammonia. Thirty minutes 
boiling is sufficient to bring to neutrality a solution having a 
strong excess of NH 4 OH. 

By saturating NH 4 OH with H 2 S, NH 4 SH is obtained. By 
oxidation of the air or by dissolving free S this is converted to 
polysulfide known as NH 4 S X . NH 4 SH is colorless. As a pre¬ 
cipitant, or a solvent for sulfides it is to be preferred to NH 4 S X , 
as it contains only the ions which enter into the reaction. During 
the reaction some yellow polysulfide is formed, so the advantages 
of both forms are generally obtained by the use of fresh NH 4 SH 
alone. The polysulfide has the advantage that it will dissolve, 
slowly and imperfectly, SnS. SnS, however should never be 
precipitated, except as a curiosity. NH 4 S X is a beter coagulant 
for sulfides than NH 4 SH. 

When polysulfides of the fixed alkalies are treated with am¬ 
monium salts NH 4 S x is formed, but the capacity of NH 4 for S 


64 


NOTES ON CHEMICAL ANALYSIS 


is less than that of Na or K. To prevent precipitation of S it is 
necessary to add some NH 4 OH. 

Sodium and Potassium Salts.—Na salts being cheaper than K 
salts are preferred where they can be used. Many of them are 
more hygroscopic than the corresponding K salts. 

NaOH takes up water from the air more readily than KOH, 
and is less convenient to handle. NaN 0 3 and Na 2 S 2 0 7 are not 
used for fusions on account of their taking up water. 

Na 2 CO s is the most used reagent for alkaline fusions, since 
it can be used in platinum. The addition of even a small pro¬ 
portion of K 2 C 0 3 notably lowers the melting point. 

NaSH is more easily obtained than KSH, and is therefore 
used as a solvent for sulfides, but KSH, made by saturating 
KOH with H 2 S, is preferable because Na makes an insoluble 
antimonate and K does not. 

KOH is as good a solvent for sulfides as KSH, but some 
KSH should be used with it to convert such compounds as 
chlorsulfides into normal sulfides and keep the metallic elements 
in their analytical places. 

When K salts are used as coagulants they must be in a con¬ 
centration of at least 5 per cent to be effective. Na salts should 
be in the same molecular concentration, though with a propor¬ 
tionately less percentage. 

Stock Alkali Solution.—Make a solution containing 5 per cent 
KOH and 5 per cent of K 2 S 0 4 and pass H 2 S long enough to 
saturate about 1/10 of the KOH. If K 2 S 0 4 is not on the shelf, 
use 36 grams of K 2 S 2 O t and 66 grams of KOH per liter, which 
will give the same solution. Let the solution stand for several 
days to settle out impurities, decant and use to dissolve sulfides. 

This solution is almost as strong as a paper filter will bear. 
If it is used as a washing solution when a precipitate is inclined 
to run through the filter, it must not be diluted, as at least this 
much neutral salt is needed if it is to be of any use as a co¬ 
agulant for precipitates. 

Sulfuric Acid.—Reagent H 2 S 0 4 has a specific gravity of about 
1.84, 95.6 per cent H 2 S 0 4 , 1,759 grams H 2 S 0 4 per liter and 35.9 
normal. 


REAGENTS 


65 


In dilute solution it has the acidity of a monobasic acid, being 
ionized as H-HS 0 4 , so that its solvent action is half what its 
normal value would indicate. In neutralization and precipita¬ 
tion it forms normal salts in most cases, both of its H ions being 
displaced. 

In concentrated solution it is a more powerful solvent for 
many elements than when more dilute. When heated it is also 
an oxidizing agent, decomposing with metals and converting them 
to sulfates. 

Much of its action depends on its strong affinity for H 2 0 , on 
account of which it decomposes organic compounds, withdraw¬ 
ing the elements of water from them. It is saturated at about 
eight volumes of water, which should be the minimum addition 
in diluting the concentrated acid. 

Sulfates are never volatile as such. They either remain in¬ 
volatile on ignition or else decompose, setting free S 0 3 , and 
allowing the remaining oxides to behave according to their 
character. Sulfates, therefore, are to be preferred in most cases 
to chlorides for ignition, and the S 0 4 ion should be used as the 
coagulant in washing solutions rather than the Cl ion, when pre¬ 
cipitates are to be ignited. 

Nitric Acid.—Reagent HNO s has a specific gravity of 1.42, is 
69.8 per cent HN 0 3 , 991 grams HNO s per liter, and is 15.7 
normal. 

HN 0 3 itself is a powerful oxidizing agent in concentrated 
solution, decomposing to NO in presence of metals or sulfides 
and forming oxides or nitrates. It decomposes HC 1 as aqua 
regia, setting free Cl. In cold solution as dilute as 5 per cent it 
has little or no oxidizing power. 

With the exception of HNO s , nitrates are not volatile, but de¬ 
compose on heating, leaving oxides. The NO s ion, therefore, is 
a good coagulant for washing precipitates preparatory to ignition. 

The solvent power of HNO s is low for elements such as Fe 
whose salts tend to hydrolysis, though all normal nitrates are 
easily soluble. 

KN 0 3 is the best oxidizing flux for use with Na 2 CO s in plati¬ 
num. It does not injure the crucible though it dissolves some of 


66 


NOTES ON CHEMICAL ANALYSIS 


it. It has the advantage over NaN 0 3 that it lowers the melting 
point of the fusion and stays dry in the shelf bottle. 

Aqua regia reacts alone as follows. 

HNO s + 3 HC 1 = 2 H 2 0 + NOC 1 + Cl 2 . 

As reagent HC 1 is 12 normal and HNO s is about 16, the proper 
proportions for aqua regia are four parts HC 1 by volume to one 
part HN 0 3 . In dissolving metals it is generally desirable to 
convert them to chlorides. The two acids should then be calcu¬ 
lated separately, from the equations. 

2 HN 0 3 = H 2 0 + 2 NO + 0 3 . 

3 Sn + 4 HN 0 3 = 2 H z O + 4 NO + 3 Sn 0 2 . 

3 Sn 0 2 + 12 HC 1 = 6H z O + 3 SnCl 4 . 

The problem is worked as follows. 

Since 2 HNO s yield 3 of O, the equivalent of 6 of H, the 
normality of HN 0 3 as an oxidizer is three times that as an acid, 
or 47.2. 


Grams Sn 

Cc. normal 

Cc. reagent HN0 3 

Cc. reagent HC1 

119 

4000 




“47-2” 

I 



12 


I 

I 

(33-6) 

(°-7) 

(2.6) 


The minimum amount of HN 0 3 , 0.7 cc. per gram, should be 
taken, with an allowance for incidental decomposition by HC 1 
and for evaporation ,and the necessary solution excess added to 
the 2.6 cc. of HC 1 . For small amounts of metal the incidental 
losses are large in proportion to the part reduced by the metal 
itself, but in dissolving large masses of metal the calculation is 
of use. 

Hydrofluoric Acid.—HF is one of the most powerful solvents, 
particularly for Si 0 2 , and must be used in gold, platinum or 
wax containers. 

It is a gas dissolved in water, its concentration as a reagent 
being about 72 per cent. On boiling it loses about half its HF. 
As a solvent, therefore, it is more active when cold or slightly 
warm than when hot. 














REAGENTS 


67 


HF assists in the oxidation of metals by HN 0 3 by dissolving 
them when oxidized, but it does not react with HN 0 3 to form 
the equivalent of aqua regia, and the two acids can be safely 
used together in gold or platinum dishes. This property is par¬ 
ticularly useful in dissolving metallic tungsten and silicon alloys, 
which do not dissolve in other acids. 

SiF 4 , formed by dissolving SiO z in HF, is a gas, easily volatile. 
If the Si is once combined with F, its expulsion by evaporation 
of the acid solution to dryness is certain. If solution is complete, 
one evaporation and ignition is enough. Attention should there¬ 
fore be directed to solution rather than to expulsion. Sand, for 
instance, requires long digestion rather than many expulsions. 

Fluorides of metals are less volatile than chlorides. It is cus¬ 
tomary, however, to add H 2 S 0 4 before expelling, for safety, the 
bases being converted to sulfates. HNO a and even HC 1 may be 
used to displace HF from solution by repeated evaporation at 
water bath temperature. 

Hydrochloric Acid and Chlorides.—HC 1 is a gas dissolved in 
water. The reagent has a specific gravity of about 1.19, 37 per 
cent HC 1 , 443 grams HC 1 per liter, and is 12 normal. 

On boiling, HC 1 solutions come to equilibrium at about half the 
reagent strength from above and below that concentration. 

HC 1 is one of the most powerful solvents, particularly for 
oxides. As it loses strength on heating it is best used slightly 
warm rather than hot when its full solvent power is desired. 

Chlorides are generally more volatile than other salts, and 
should be removed from any substance preparatory to ignition. 
As the Cl ion is easily shown by AgN 0 3 , testing filtrates for Cl 
serves the double purpose of showing when soluble bases are re¬ 
moved from the precipitate, which would give high results on 
ignition, and chlorides, which would give low results. 

Chlorides of the alkalies, however, may be heated to tempera¬ 
tures below redness without loss. 

NH 4 C 1 assists better than other ammonium salts in increasing 
the solubility of salts of the alkaline earths. 

In quantitative analysis, chloride solutions are used perforce 
in H 2 S separations, since HC 1 so often has to be used as a sol- 


68 


NOTES ON CHEMICAL ANALYSIS 


vent, but the precipitates are not so easily handled as those 
formed from HNO s and H 2 S 0 4 . Chlorsulfides instead of normal 
sulfides may be formed, which tend to run through the filter on 
treatment with alkalies. The best corrective is to keep the acidity 
as low as possible. The alkali should contain sulfides, which will 
convert the chlorsulfides to normal sulfides. 

Chlorates.—KC 10 3 . is stable in HNO s solution, even when warm, 
but it is endothermic to KC 1 and the mixture is an oxidizer for 
sulfides, converting nascent S to SO s . Molar S is not acted on. 
KC 10 3 + 6 HC 1 ;= 3 H 2 0 + KC 1 + 6 Cl. 

KCIO3 is a valuable aid in dissolving metals in HC 1 , avoiding 
the presence of N compounds and the danger of forming volatile 
H compounds such as arsene. The free Cl is easily removed by 
boiling. 

KCIO3 acts as an oxidizer in boiling solutions on metals tend¬ 
ing to oxidation such as Fe, when the solution is barely acid. In 
the case of Fe the acid set free by the hydrolysis of a neutral 
salt is sufficient to decompose KC 10 3 . 

Bromides and Bromine.—The properties of HBr are similar to 
those of HI, but it is slightly exothermic, and it is used in re¬ 
duction only for elements which have a decided preference for 
the lower valence. 

Bromine is a useful oxidizing agent, since it is obtained pure 
in liquid form. It converts S to SO s and Mn to MnO a . For the 
former purpose its action is increased by dissolving it in an 
organic liquid, such as CC 1 4 , as suggested by Allen and Bishop. 
A. M. Smoot improved this by using acetic acid, which allows 
mixture with water. His mixture is Br four parts, HC 2 H 3 0 2 
six parts, H z O one part. Allen and Bishop now use a concen¬ 
trated water solution of Br with KBr. 3 

HBrOg is endothermic to HBr, and is therefore a useful oxi¬ 
dizer of low power. In hot HC 1 solutions it bleaches methyl 
orange, by which excess is shown, and therefore it can be used 
in titrations. In separations it is not much used on account of 
the variable stability of the bromides produced. 


3 Scott, “Standard Methods of Chemical Analysis.” 


REAGENTS 


69 


Hydriodic Acid and Iodides.—HI is not kept as a reagent on 
account of its instability, but freshly formed by the acidulation 
of iodides it is valuable because it is endothermic and assists in 
the reduction of elements from a higher to a lower valence, and 
at the same time liberates I which can be titrated. As its re¬ 
ducing action is weak, the extent of the reaction is controlled by 
the element reacting with it, with the result that the other element 
is reduced to a definite valence which is stable, making titrations 
accurate. 

Hydro sulfuric Acid and Sulfides.—H 2 S is a weak acid, slightly 
ionized as H—HS. It forms acid sulfides with strong bases, 
such as KHS (or KSH), and normal sulfides with weak bases, 
such as PbS. 

Water saturated with H 2 S at room temperature is about 0.25 
normal. One cc. will precipitate eight milligrams of Cu. 

Coming from the generator, H 2 S is likely to carry some Fe. 
By bubbling the gas through water this can be effectively re¬ 
moved. 

Air and the elements which it reduces during precipitation 
cause H 2 S to be partly converted to H 2 S 0 4 , so that the presence 
of that acid is to be counted on after an H 2 S treatment. 

Reactions with NH 4 OH are noted under Ammonia Water. 

NaSH is obtained in crystals. KSH is not. Polysulfides of 
both bases are obtainable, though KS X , ordinarily called potas¬ 
sium sulfide, is more common. 

Acetic Acid.—HC 2 H 3 0 2 is obtained as glacial acid, 99.5 per 
cent pure, 17.5 normal. 

Another commercial strength is specific gravity 1.044, 3 2 -5 
per cent pure, 5.6 normal. 

HC 2 H 3 0 2 is a very weak acid, and when its salts are added 
to stronger acids the acidity of the mixture is that of the 
HC 2 H 3 0 2 liberated. 

Tartaric Acid.—H 2 C 4 H 4 0 6 is a dibasic acid which is ordinarily 
half ionized, forming bitartrates. It is obtained in crystalline or 
powdered form. Its principal use in analysis is to prevent the 
precipitation of hydrates, as most metals form with it double 
salts soluble in alkalies. 


70 


NOTES ON CHEMICAL ANALYSIS 


While it keeps hydrates in solution, it does not interfere with 
the precipitation of sulfides. Elements such as Fe, which form 
insoluble sulfides, are easily separated by its use from elements 
such as Al, which do not. 

With its aid Sb may be brought into solution when sulfides 
are decomposed or metals dissolved with HN 0 3 , and it may be 
kept in solution without the large excess of mineral acid which 
would otherwise be necessary. 

If tartaric acid is used in the early part of a complete analysis 
it is necessary to destroy it before Group 3 can be separated. 
This can be done in the wet way by adding HNO a and H 2 S 0 4 , 
evaporating to fumes of SO s , and completing the oxidation by 
further additions of HN 0 3 . If much tartaric acid is present a 
large beaker is necessary, as a heavy froth arises. 

Oxalic Acid and Oxalates.—H 2 C 2 0 4 . 2 H 2 0 is obtained in crys¬ 
tals which are stable in air, and may be used as a standard against 
volumetric alkaline solutions and KMn 0 4 . 

In the presence of this acid, aided by its ammonium salt, 
tetravalent Sn forms a soluble sulfide. This permits the separa¬ 
tion of Sn from the other elements of its group. In this con¬ 
nection it is worth noting that the oxalates of Cu, Pb and diva¬ 
lent Fe are but slightly soluble in water or dilute acid, and special 
precautions are necessary to keep them in their analytical places 
during the H 2 S separation. 

(NH 4 ) 2 C 2 0 4 .H 2 0 is the most commonly used precipitant 
for Ca. 

Na 2 C 2 0 4 can be obtained from the U. S. Bureau of Standards 
in great purity without moisture, and is the best standard for 
KMn 0 4 solutions. 

Cyanides.—KCN and NaCN are useful for keeping the three 
colored elements, Cu, Ni, and Co, from precipitating as sulfide 
in alkaline solution, permitting their separation from Cd, Bi, Zn, 
etc. 

As these three elements are decolorized by cyanides titration 
methods are possible. 

Care should be taken in the use of cyanides to avoid acidulat¬ 
ing their solutions in the open room, on account of the volatile 
and poisonous HCN. 


CHAPTER V 


FUNDAMENTAL OPERATIONS 

Precipitation.—A precipitate is something more than an insol¬ 
uble substance. Its particles have more or less cohesion, which 
enables them to bridge over the pores in filters and remain while 
the solution passes through. They form a more or less porous 
mass which itself may act as a filter or in different degrees clog 
the filter. 

The aim of the analyst is to produce precipitates which remove 
as much as possible of given elements or compounds from 
solution in forms which are easily filtered and washed. Having 
a solution containing an element which he wishes to precipitate, 
he must satisfy several conditions. 

1. Valence .—The proper oxidizing or reducing reactions are 
produced, if the element is not already of a suitable valence. 

2 . Precipitant .—This is chosen with regard to the quantity 
necessary for complete precipitation, a slight excess being neces¬ 
sary in some cases and a large excess in others. 

j. Conditions of Insolubility and Cohesion .—These include 
the regulation of acidity or alkalinity, heat, pressure, particu¬ 
larly when the precipitant is a gas, agitation, time, and the pres¬ 
ence of electrolytes in the solution called coagulants, which 
cause the precipitate to cohere. 

In devising a scheme for a precipitation, every one of these 
points must be considered, both with respect to the desired ele¬ 
ment, and also to the prevention of undesired occlusions. The 
theory of solutions is of value for suggestions in regard to 
proper conditions, but the obscure peculiarities of the different 
elements require experiment and observation for their accommo¬ 
dation. A few general rules may help. 

Rules for Precipitation.—Crystalline precipitates filter best when 
the crystals are large. They need time in which to grow; either 
by slow precipitation, or by producing temporarily a condition of 
slight solubility, during which the larger crystals, being less sol¬ 
uble, grow at the expense of the smaller. This may be brought 


72 


NOTES ON CHEMICAL ANALYSIS 


about in some cases by boiling, in others by gradual addition of 
reagents, in others by agitation. 

Amorphous salts, such as sulfides and hydrates, cohere best 
in the presence of electrolytes, such as acids and ammonium 
salts. Precipitates of this class which are hardest to filter are 
helped by giving them time to settle. 

An occasional failure of a precipitation may be caused by 
overlooking the fact that in the ordinary course of analysis, by 
the neutralization of acids and alkalies, large quantities of salts 
are introduced, while in a shortening of the scheme the solution 
may be almost free from them, so that they need to be added in 
order to form a filterable precipitate. 

Filtering.—The object of filtering being to separate a solid 
from substances in solution, the maximum of efficiency consists 
in driving the original solution through and out of the solid by 
means of a washing solution, with the least amount of mixing 
of the two liquids. 

For all porous substances, such as crystalline precipitates, the 
most efficient form of filter is that in which the solid is collected 
in a layer of uniform thickness and the washing moves in a 
direction normal to it. The Gooch crucible and the plate filter 
fulfill these conditions perfectly, and they are therefore to be 
preferred if other conditions permit. The volume of washing 
solution necessary is much less than that for conical filters. 

Such filters are generally used with suction, but by attaching 
a tube to the holder, three millimeters in diameter and about a 
meter long, or reaching from the table to the floor, the filtration 
of crystalline precipitates without suction is practicable. By the 
use of such tubes the filtrate may be received in a beaker, thus 
saving volume of washings. For some classes of work a set of 
ten or more such holders in a rack is a useful adjunct. 

The Paper Filter.—In using a conical paper filter it is necessary 
to keep in mind the fact that the procedure for an empty paper 
is quite different from that for a large precipitate. In washing 
an empty filter, since draining is rapid, the washing solution tends 
to run over the upper part of the paper and out at the tip. Air 
bubbles prevent the washing from reaching the paper back of 


FUNDAMENTAL OPERATIONS 


73 


them. Therefore the jet must be directed into the paper, either 
from the top, loosening the folds and allowing the solution to go 
between them, or else against every part of the upper half, and 
particularly at bubbles. 

A good practice test of washing an empty paper is to saturate 
it with K 2 Cr 2 0 7 solution and form a routine method that is 
amply sufficient to wash it out. 

Washing by Decantation.—A paper half-filled or more with pre¬ 
cipitate drains more slowly, and washing the top clean is generally 
sufficient to insure that all the paper is well washed. But in this 
case the path of least resistance, instead of being through the 
bottom, goes around the tip of the paper, and if the precipitate 
tends to clog, no amount of washing will get all of the filtrate out 
of the tip. The proper procedure is to wash the beaker, and 
without waiting for the filter to drain, wash around the top of the 
filter. Then wash not more than twice more, enough to get the 
top of the paper clean. Now return the precipitate to the beaker. 
If it is coherent, use the rod or tube, not the wash-bottle, getting 
out as much as possible without breaking the paper. Now add a 
few drops of water at a time and mix it into the precipitate. 
After a soft paste has been formed so that more water can be 
easily stirred in without leaving lumps, wash out the filter, all but 
thin layers, add as much water as will fill the filter once or a little 
more, add such reagents as are necessary to keep the precipitate 
coherent and insoluble, and filter and wash as before. One 
decantation of this sort is enough for a sulfide or hydrate pre¬ 
cipitate which does not fill the paper more than one-third full, 
and three when the paper is entirely filled. 

Washing Solutions.—When precipitates tend to disintegrate and 
run through the filter, boiling hot water is better than cold or 
warm water for washing. Allowing the precipitate to stand after 
draining increases the tendency to run through. 

Addition of the precipitant to the wash-water is sometimes 
enough, but it is better to add also a coagulant which does not 
interfere with the use of the precipitate. The ammonium salts 
are the best coagulants, as they need not be added in large pro¬ 
portions to be effective. Sodium or potassium salts must be 


74 


NOTES ON CHEMICAL ANALYSIS 


at least 5 per cent of the solution to be worth adding. Acids in 
slight proportions are effective when the precipitate is insoluble 
in acid. Generally the addition of the precipitant is unnecessary 
when the proper coagulant is used, though in some cases, particu¬ 
larly in filtering sulfides, the percipitant prevents decomposition 
by oxidation. 

A paper filter will withstand a 5 per cent solution of KOH. 
If a somewhat stronger solution needs to be filtered, the paper 
should be reinforced by gauze. An acid or alkaline solution strong 
enough to dissolve cellulose should be filtered on asbestos. 

Reprecipitation.—In some cases perfect washing is impossible, 
on account of the cohesiveness of the precipitate or its occlusion 
of impurities. Reprecipitation is the remedy. When this is 
necessary, the star fold is a hindrance, and the ordinary form is 
better. It is generally easier to control the conditions for the 
second than for the first precipitation, and one should therefore 
make sure that not only the precipitant, but also a coagulant, is 
present in proper proportions. The coagulant is generally formed 
by neutralizing the solvent with the precipitant, but if not enough 
of the solvent has been used, the precipitation may not be satis¬ 
factory. Therefore one should be not content with a minimum 
of the solvent, but should make sure that an effective coagulant 
will be present. 

Destroying Organic Matter by Acid.—Paper and other organic 
matter, even coke, but not graphitic carbon, is easily oxidized and 
removed by the combined action of HNO s and H 2 S 0 4 . Enough 
H 2 S 0 4 should be present to cover the bottom of the beaker; the 
more the better, but the needs of the analysis generally limit the 
amount. 

The more organic matter the larger the beaker, as a heavy 
froth may form which rises remorselessly. One gram can be 
destroyed in a 250 cc. beaker with 5 cc. of H 2 S 0 4 . To destroy 
an eleven centimeter filter add 10 cc. of HN 0 3 and boil down 
rapidly to fumes of S 0 3 . When the acid turns black add more 
HN 0 3 through the lip of the beaker with a pipette or thin tube, 
repeating the additions until the color disappears. Pyrex beakers 


fundamental, operations 


75 


will not crack under this treatment. Jena beakers used to crack 
occasionally. Some (NH 4 ) 2 S0 4 is formed by the reaction. 

During this treatment some nitrosyl sulfuric acid is formed, 
which is not driven out by fuming. On dilution it forms nitrous 
acid. This must be expelled by boiling for about five minutes 
before passing H,S, otherwise a continuous decomposition of 
the HoS may be started. In order to remove N compounds com¬ 
pletely preparatory to the electrolysis of Cd, Ni, etc., the acid 
must be diluted slightly and evaporated to fumes two or three 
times. 

Rapid Evaporation of Solutions.—Solutions in beakers can be 
evaporated more rapidly on a hot plate than on the water-bath, 
if left uncovered and heated just short of boiling. 

Evaporation is more rapid if a piece of glass rod, bent into 
the shape of a fish hook, is put on the edge of the beaker under 
the cover on the side away from the lip, and the solution boiled 
rapidly. A beaker almost full boiled in this way has no tendency 
to bump, as it does when tightly covered. 

The speed of evaporation is increased by laying an inverted 
cover, a size smaller, on top of the other. This makes an air 
space and decreases the condensation on the cover. 

When solutions containing large amounts of salts are evapor¬ 
ated to fumes with H 2 S0 4 , the critical point, when spitting is 
likely to occur, is when the salts are forming into a cake. A very 
low heat is necessary at this point. Adding the H 2 S0 4 at a con¬ 
centration not quite enough to form the cake and evaporating 
on the water-bath until the cake is formed, finishing on the hot 
plate, saves attention. 

METHODS OF DECOMPOSITION 

Alloys.—Most alloys respond best to a preliminary acid treat¬ 
ment, the choice of acids depending on the major constituents. 

HC1.—All metals except silver form soluble chlorides, but those 
electro-negative to hydrogen do not dissolve in HC1 without an 
oxidizer. It is often advantageous, as in the case of alloys high 
in Pb, to boil the finely divided sample with concentrated HC1 
until it is entirely decomposed, leaving a residue of Sb, Cu, etc. 
The beaker is then removed from the heat, and KC10 3 stirred 


76 


NOTES ON CHEMICAL ANALYSIS 


in a little at a time until there is free Cl in excess, which is then 
boiled out, leaving a clear solution. While PbCl 2 has a low 
solubility in cold HC 1 solutions, it is easily soluble when hot, 
and Pb dissolves as readily as its position in the electro-potential 
series indicates, if enough solution is provided to keep the PbCl 2 
from covering the undecomposed alloy. 

Since PbCl 2 crystallizes from acid solution in great purity, it 
is often convenient to separate the bulk of the Pb in this way 
before proceeding with the analysis. 

Lead Chloride Separation.—Boiling HC 1 reaches constant com¬ 
position at about 50 per cent of its reagent strength, whether 
weaker or stronger before. At about 20 per cent the solution 
holds the least Pb per unit of HC 1 . Therefore to separate 
PbCl 2 it is best to concentrate the HC 1 solution to 20 or 30 cc., 
or until PbCl 2 begins to separate, add double its volume of water, 
and allow it to cool, best over night. The PbCl 2 is then filtered out 
and washed with cold 5 per cent HC 1 . No more PbCl 2 will sepa¬ 
rate in the filtrate unless it is further concentrated. 

Aqua Regia.—Aqua regia is theoretically composed of three 
parts HC 1 and one part HN 0 3 , but in practice it is better to 
calculate the amount of HNO s necessary to oxidize the sample by 
its decomposition to NO, adding a slight excess over that, enough 
HC1 to give the desired excess, and enough water to keep the 
action from being too violent. The typical reaction is as follows. 
2 HN 0 3 + 3 Cu = 3 CuO + H 2 0 . 

Combining this with HC 1 we have, 

2 HN 0 3 + 6 HC 1 + 3 Cu = 3 CuCl 2 + 2 NO + 4 H 2 0 . 

Aqua regia is particularly useful for alloys high in Sn, which 
do not dissolve in HNO s , and in which there is danger of losing 
some As as AsH 3 and possibly Sb as SbH 3 when dissolved in 
HC 1 alone. Also the solution is completely oxidized and free 
from alkali salts. When such an alloy is treated with aqua regia, 
the Sn dissolves first to a colorless solution, the electro-negative 
elements precipitating upon it. The solution is quiet until all Sn 
is dissolved, and then the precipitate dissolves, sometimes with 
explosive violence. It is necessary to use a large beaker and 
to have a pan of water ready to check the reaction. 


FUNDAMENTAL OPERATIONS 


77 


Alloy Mixture.—A good mixture to dissolve any SnPb alloy 
is composed of H 2 0 40 cc., HC 1 30 cc., and HNO s 4 to 5 cc. 
This will dissolve a gram of Pb by simmering or gently boiling 
for half to three-quarters of an hour. 

A good mixture for ten grams of tin alloy is 25 cc. water, 50 
cc. HC 1 and 15 cc. HNO s , in an 800 cc. beaker. 

HN 0 3 ,—All alloys low in tin and antimony may be dissolved in 
HN 0 3 , the Sn remaining almost undissolved as metastannic acid. 
Sb forms an equivalent compound, and if there is four times as 
much Sn as Sb, the Sb will also be completely precipitated, 
though when alone its solubility is considerable. As in small 
proportions is also held by metastannic acid, and also part of 
the Fe, Mn and Cu. Most other elements are completely soluble 
under these conditions, except that PbS 0 4 may be formed by 
the oxidation of S in the sample. This can be prevented by 
using an equal amount of water with the HNO a . There are 
many schemes for the complete separation of Sn from other 
elements by HNO s , but in the writer’s experience none of them 
are successful, the precipitation of Sn is never complete, the pre¬ 
cipitate is never pure, and the complete separation of Pb by 
diluting the HN 0 3 is more important than any other consid¬ 
eration. 

High Oxidation Mixtures.—HNO s with a little HC 1 is useful 
for oxidizing S in some alloys. A saturated solution of KC 10 3 
in HN 0 3 is more efficient. The concentration may be increased 
by dissolving the salt to saturation on the water-bath, as the two 
compounds do not decompose each other even when heated. The 
solution should be cooled before use, and the reaction with the 
sample should be retarded by moving the beaker about in a pan of 
water. The full amount of the mixture should be added at once, 
as when the KC 10 3 is not in excess the reaction proceeds with 
HNO s alone, as is shown by the presence of red fumes, and the 
oxidation of S may not be complete. 

Bromine alone is not useful on account of its volatility. In 
combination with HN 0 3 or HNO s plus a little HC 1 , it helps 
the oxidation some. Its best use, howover, is in solution with 
an acid, in which form it is less volatile and makes a better con- 

6 


78 


NOTES ON CHEMICAL ANALYSIS 


tact with the sample than when used alone. A. M. Smoot uses 
a mixture of two parts bromine and three parts acetic acid. 
This mixture will convert crystals of sulfur to sulfuric acid. 
The sample should be allowed to stand cold in contact with the 
mixture for several hours, and then treated with some other 
acid. 

H 2 S0 4 .—Dilute sulfuric acid dissolves only those metals which 
are electro-positive to H. Lead, though in this class, is kept from 
dissolving by a coating of PbS0 4 which forms quickly. On 
account of its high normal value and the low solubility of many 
of its compounds it is best used in dilute solutions, about one 
part in ten. 

Hot concentrated H 2 S0 4 is a powerful oxidizer, all but the 
noble metals decomposing it and forming sulfates. It is par¬ 
ticularly useful for the treatment of alloys for volumetric work, 
in which nitrates must be avoided. Its action is helped by the 
addition of K 2 S 2 0 7 , which raises its boiling point and allows a 
higher temperature in an open vessel. The products of this 
reaction, if not soluble on dilution, will dissolve easily on the 
addition of HC1. 

Solution in Alkalies.—Aluminum alloys are conveniently dis¬ 
solved in NaOH or KOH. This is not only a better solvent than 
any acid, but it has the advantage of concentrating most of the 
other elements in the insoluble residue. The danger of frothing 
should be guarded against. 

ORES, ACID TREATMENT 

Sulfides.—Some sulfides are decomposed by HC1, but in most 
cases where its use is theoretically possible, as for instance in the 
treatment of stibnite, there is generally some good reason for not 
using it. In the case of stibnite, weathering often forms oxides 
insoluble in HC1, and the residue requires a separate treatment. 
As it is just as easy and somewhat safer to fuse the whole 
sample, the use of HC1 is not advisable except for samples of 
known purity. 

Nitric acid decomposes all sulfides with liberation of sulfur. 
As tin seldom occurs as sulfide it is not likely to be found in 
the nitric acid solution of an ore, though tin from stannite will 


FUNDAMENTAL OPERATIONS 


79 


dissolve. The addition of tartaric acid permits the solution of 
stibnite in HNO s , though the objection to its use is the same 
as for HC1. 

Sulfuric acid is seldom used to decompose sulfides directly, 
though it is useful in combination with HNO a , the latter being 
driven off by evaporation after the ore is decomposed, convert¬ 
ing the soluble portion to sulfate. When a mixture of HN0 3 
and H 2 S0 4 is used, it is generally best to add an equal volume 
of water, which gives a better solvent effect. 

Oxides.—HC1 is by far the best solvent for oxide ores contain¬ 
ing much iron. When an ore is to be completely decomposed for 
analysis, the start is generally made with HC1. 

HNO s is used as the solvent for the assay of ores of Cu, Zn 
and other elements whose oxides are easily soluble in it. It is 
convenient, because the same mixture can be used for all ores 
of these elements, whether oxide or sulfide. 

Sulfuric acid is used to drive off HNO a as for sulfides, but 
seldom for direct decomposition. 

Mixed Ores.—Hydrofluoric acid is often useful for liberating 
some element from combination with or occlusion by SiO z . It 
is not always necessary to dissolve all of the silica, as the desired 
element may be in fissures in the quartz, and the acid, by dis¬ 
solving the silicates, will search out the pores, leaving pure 
quartz. HF treatment is conveniently done in a platinum or 
gold dish, H 2 S0 4 being used to drive off the more volatile acid 
after it has done its work. 

When it is necessary to dissolve ferric oxide and also to decom¬ 
pose sulfides, it is better to use HC1 first, following with HN0 3 . 
The solvent action of HC1 on oxides is much greater alone than 
in combination with HN0 3 , while the oxidizing action of HNO s 
is helped by the presence of HC1. The solvent power of HC1 is 
greater when it is slightly warmed, but not heated enough to 
weaken it by evaporation. 

Slags and Soluble Silicates.—Slags are often so high in silicates 
that if acid is poured on a sample and allowed to stand a cake is 
formed which hinders decomposition. This trouble is prevented 
by dissolving the silicic acid as it forms. 


8o 


NOTES ON CHEMICAL ANALYSIS 


To a gram of slag add 25 cc. of boiling water and then, while 
shaking, 10 cc. of HC1, a little at a time, keeping the sample in 
motion until it is nearly or quite dissolved. By adding more 
water and adding the acid while the water is boiling less manipu¬ 
lation is required. After the action of the HC1 has ceased, add 
5 cc. of HN0 3 to dissolve sulfides and oxidize iron, boil until 
SiO z begins to separate, and evaporate to dryness on the water- 
bath. 

If it is desired to separate the H 2 S group only, use 100 cc. of 
water per gram of sample, HC1 in slight excess, no HNO s , boil 
only until the solution of silicates is complete, pass H 2 S and 
filter hot. The more soluble slags are easily handled in this way 
without separating the Si0 2 . 

Insoluble Residues.—After the acid treatment it is often neces¬ 
sary to separate the residue and treat it differently, generally by 
fusion, though sometimes by HF as above. 

The residues insoluble in acids are generally themselves of acid 
nature, and require alkaline treatment. This is more easily given 
by fusion than in the wet way, not only because a stronger action 
is so obtained, but because alkaline solutions attack most con¬ 
taining vessels. 

Filtration of the Insoluble Residue.—The residue may consist 
in part of gelatinous silica from the decomposition of silicates. 
For this reason all ores are thoroughly dehydrated before filter¬ 
ing. If H 2 S0 4 has been used, the acid is heated enough to give 
white fumes of S0 3 , showing that not only the HN0 3 but also 
the water has been expelled, making the silica insoluble. 

In other cases, the sample is evaporated to dryness and baked 
at a temperature somewhat above ioo° to make sure of dehydrat¬ 
ing the silica. This baking is more safely conducted on a plate 
heated by gas than is the case after fusion, as there are no alkali 
salts present which might form soluble silicates. Account must 
be taken here of the volatility of FeCl 3 under these conditions. 
If Fe is to be determined, the heat should be under thermometer 
control in an oven. 

After drying, in most cases HC1 is used to take up the soluble 
portion. After warming the concentrated acid, water is added. 


fundamental operations 


8i 


The filter must be arranged with care, for the residue is not a 
precipitate, unless it consists partly of decomposed silicates, and 
may not cling to the filter. The paper should be folded in the 
ordinary way, without tearing ofif the corner, and some pulp 
should be poured in around the top, to close the channel at the 
back and keep the column, as well as to reinforce the paper. In 
most cases water is used for washing, but acid may be necessary, 
as in the treatment of zinc retort cinder, to keep the residue from 
running through. As a general thing, HC1 should not be used to 
wash a residue for ignition, as so many chlorides are volatile. 
HN0 3 i s better, or H 2 S0 4 may be used. 

Some residues, such as those of waste products containing Sb, 
will suffer loss by reduction to volatile forms on ignition of the 
paper. They may, if the elements of asbestos are not the sub¬ 
ject of the assay, be filtered on a Gooch crucible, the mat dried, 
removed and fused with the residue. For this purpose a holder 
that transmits the filtrate safely is necessary. 

Choice between Fusion of the Entire Sample and Fusing the 
Insoluble Residue.—When the residue can be ignited without 
loss it is generally preferable to treat the sample with acid first 
and fuse the residue with Na 2 CO s in platinum. 

It is hardly ever worth while to fuse with K 2 S 2 0 7 a residue 
insoluble in acid. Such a residue needs an alkaline flux. 

The combination method permits the use of a larger sample 
than the fusion alone will accommodate, protects the major part 
of it from the vicissitudes of the fusion, and allows the use of 
platinum with more safety. The principal objection is that it 
takes no more time to fuse the sample from the start than to fuse 
the residue alone, so that time can be saved by fusion, particularly 
when Na 2 0 2 is used as the flux. 

The Bisulfate Fusion.—K 2 S 2 0 7 , ordinarily called bisulfate, may 
be fused in platinum, silica or porcelain. It has a slight solvent 
action on platinum, but none on silica or porcelain. Porcelain 
is particularly adapted to this flux, as the smooth sides of the 
crucible permit the melt to be dropped out after cooling. The 
crucible must be protected against drafts while hot, but aside 
from that its tendency to crack is less than that of silica. 


82 


NOTES ON CHEMICAL ANALYSIS 


The pyrosulfate should be thoroughly dehydrated. Old ma¬ 
terial should be remelted before use. It may be added in large 
pieces, though quicker and more complete action is obtained by 
mixing the residue with the powder. The heat should be grad¬ 
ually increased, so that the excess acid may not be driven off too 
soon. The rule is to apply just enough heat to keep it melted, 
raising the heat from time to time when it begins to harden, 
until the full heat of a Bunsen burner is necessary for fusion, 
the finish being at a bright red heat. An outer crucible should 
be used at first, and removed when high heat is required. This 
flux does not automatically wash down the sides of the crucible. 
If any of the residue is above the surface, the crucible should 
be manipulated to cover it with the flux and bring it under. A 
dark-colored residue is easily seen through a porcelain or silica 
crucible if a white light is held below, so it is possible to tell 
how the fusion is proceeding. It should occupy a full hour. 
When the lid is removed for examination, it should not be in¬ 
verted, as the spatter or distillate is very liquid. 

The melt should be allowed to cool quietly. When cold, hold 
the crucible over a beaker and clap it sharply against its lid. This 
will loosen the bulk of the precipitate. Let it fall into the beaker. 
The crucible should then be filled with hot water, covered with 
its lid and allowed to stand a few minutes, when it can be washed 
out into the beaker. A little extra acid helps the leaching. 

The bisulfate fusion is essentially an acid treatment, and is 
suitable only for oxidized material, either ignited precipitates, 
oxide ores or residues which have been treated with HF. 

Sodium Carbonate Fusion.—A platinum crucible is generally 
used for this fusion, though nickel can be used. It is important 
to avoid substances which will injure the crucible. Lead in most 
cases can be removed by HC1, unless there is a combination of 
Pb and Sb. The addition of a little KN0 3 will generally protect 
the crucible against alloying, by keeping the metals oxidized. It 
is during the ignition of the paper that most of the alloying 
occurs, and this may be done in porcelain in case of doubt, and 
the residue after thorough oxidation transferred to the platinum 
for fusion. Even litharge can be fused in this way in platinum 
without alloying, though an adherent coating may form. 


fundamental operations 


83 


The result of the sodium carbonate fusion is to convert all 
silica and other acid radicals into sodium compounds soluble in 
water. Alumina is slowly converted to sodium aluminate, re¬ 
quiring in some cases long heating at blast temperature. It is 
the best flux for fused alumina, which is practically insoluble in 
acids. 

Before cooling the melt, it should be put into better form for 
solution than when left in the bottom of the crucible. It may be 
poured into a platinum dish floating in water. If the melt is not 
too large, it can be poured into the lid of the crucible, supported 
level on a porcelain crucible. For this purpose there should be 
no crack in the lid, or the melt will find it and run through. 

The writer prefers to rotate the crucible while cooling, since 
this leaves the melt in a thinner layer than when poured. As it 
is best to dissolve the melt entirely before acidulating, no time 
is lost, though it may take longer to get the crucible clean. 

After the melt has hardened, the crucible is put into a platinum 
dish or porcelain casserole and leached out with the least amount 
of hot water. It is easier to get the crucible clean if it is entirely 
leached and policed before acidulating. Then the oxides are 
dissolved by filling the crucible with acid, pouring this into the 
carbonate solution. 

Niter and Soda Fusion.—The technique of this fusion is the 
same as that of the sodium carbonate fusion, except that it must 
be leached in porcelain, or else acidulated with HNO s to avoid 
dissolving the platinum dish. The same precaution applies to the 
ordinary carbonate fusion if any KNO s has been added. The 
use of this fusion is principally to convert sulfides to sulfates. 
The KN0 3 should not be more than 1/20 of the Na 2 C0 3 , and 
preferably barely enough to perform the necessary oxidation. 

Fusion Mixture.—Sodium and potassium carbonates mixed 
have a much lower melting point than either alone. The lowest 
melting point is made by mixing them in molecular proportions, 
though most of the advantage is gained by the addition of a very 
little of one to the other. By using this mixture a fusion can be 
made in porcelain with little difficulty, and easily in nickel. 


8 4 


NOTES ON CHEMICAL ANALYSIS 


Sodium Peroxide Fusion.—This fusion can be made in porcelain, 
nickel or iron, each having some advantages. 

In porcelain, no metal is introduced into the melt, which makes 
it useful for oxidizing such elements as chromium preparatory 
to titration. As the flux dissolves the crucible rapidly, the oper¬ 
ation must be so conducted as to decompose the sample without 
loss of time. It should be finely ground and well mixed with the 
flux. A cover of unmixed flux helps to prevent loss. The cruci¬ 
ble should be heated almost to fusion over a Bunsen burner. It 
may then be taken in tongs and manipulated in a large mild blast 
flame, to bring the heat up quickly and evenly. As soon as the 
flux is enough melted to flow it is rotated so as to bring in all 
of it and then heated quickly almost to the temperature at which 
it spatters. Another method is to support the crucible covered 
on a triangle, removing the lid momentarily to watch it closely 
until the flux is melted in the middle, then remove the flame 
and then the lid, finishing by manipulation over the Bunsen flame. 
The melt is allowed to harden in mass. 

In nickel or iron, since a larger crucible is used, no cover is 
necessary, and preliminary heating is not necesasry, though it 
saves time, one crucible being heated over the Bunsen flame 
while the next is manipulated over the blast. An iron or nickel 
crucible can be used safely until the bottom is flexible in the 
hand. 

These crucibles melt through the bottom more easily if the 
sample has not been well mixed with the flux or if a sharp blast 
is used, in either case raising one point to the ignition tempera¬ 
ture of iron. 

For leaching, the crucible should be laid on its side in a suffi¬ 
ciently large beaker, held in place by standing a rod in it. Cold or 
warm water is poured in just enough to dissolve the melt, allow¬ 
ing it to mix itself. 

The crucible should then be stirred in the solution before polic¬ 
ing, which makes it easier to clean. After policing, it is good 
practice to wipe it dry immediately, so that it will not rust. 


fundamental operations 


85 


If it is not necessary to keep the volume down, the crucible 
may be covered with hot water, which is better if the insoluble 
part is to be filtered in the alkaline solution. Before filtering, 
the solution should be diluted to 5 per cent to avoid breaking the 
paper, if an ordinary filter is used. 

The scales of iron or nickel from the crucible are easily 
soluble in a sufficient excess of HC1, which should be added in 
bulk to avoid precipitation of silica. Oxalic or sulfuric acid will 
dissolve the scales, though not so readily as hydrochloric acid. 

Sulfur and Soda Fusion.—It is customary to make this fusion 
with equal parts of sulfur and sodium carbonate. A better mix¬ 
ture is Na 2 C0 3 100 parts, K 2 C0 3 140 parts, and S 100 parts. 
This gives a lower melting point, and the sulfur is sufficient, as 
it is twice as much as is necessary to combine with the bases, 
the excess volatilizing quickly in any case. 

Pure amorphous oxides of tin and antimony are so easily 
fused in this flux that it is not necessary to mix them before 
heating, only enough heat to give complete fusion being neces¬ 
sary. It is an interesting experiment to use a glass cover for 
this fusion, through which its phases can be seen without ad¬ 
mitting air. The cover should be no wider than the crucible, or 
the flame will crack it. 

Such minerals as cassiterite require long fusion at the highest 
temperature of the Bunsen burner, using a chimney. Even then 
it is often necessary to filter the solution and fuse the residue. 

The melt is best leached in cold water, as this allows the sul¬ 
fides to settle and filter better than when heated. Stirring while 
leaching should be avoided. The flux is entirely converted to 
alkaline polysulfides. 

If the solution after leaching shows a green color from colloidal 
Fe, it can be cleared by adding an ammonium salt in excess over 
the Na. As the capacity of NH 4 for S is less than that of Na, it 
will be necessary to add also some NH 4 to prevent the precipita¬ 
tion of S. 

If NH 4 salts are not wanted, add Na salts, at least 10 per cent 
of the solution. NH 4 salts are more efficient in precipitating Fe, 
but increase the solubility of Cu. 


86 


NOTES ON CHEMICAL ANALYSIS 


Sodium Hydroxid Fusion.—This fusion is made in silver. In 
order to avoid loss by spattering, it is best to melt the flux in the 
crucible to drive out water, cool it, put the sample on top of the 
cake, and melt again. This fusion is good for removing gangue 
from graphite. 


CHAPTER VI 


QUALITATIVE ANALYSIS 
PREFACE 

The scheme of qualitative analysis here given is not intended 
to give methods of identifying the elements with the least amount 
of work. It is intended to show how the different elements can 
be separated quantitatively from each other, and to give practice 
in recognizing and handling them in the forms in which they 
usually appear in course of quantitative analysis. 

Quantitative analysis is a profession, or rather a trade. Quali¬ 
tative analysis is an occasional expedient. It is generally per¬ 
formed by one whose occupation is quantitative analysis, and who 
will naturally use the methods with which his daily work keeps 
him familiar. 

By following as closely as possible ordinary quantitative pro¬ 
cedure in qualitative analysis, the student will gain the practical 
knowledge which he will be able to use in any analytical work; 
he will be able to turn any qualitative test into a quantitative test; 
he will avoid cumbering his mind with information of little use. 


88 


NOTES ON CHEMICAL ANALYSIS 


QUALITATIVE ANALYSIS 

GENERAL SCHEME 

Reagents.—When quantities of reagents are mentioned, they 
are understood to be in the form in which chemical houses sup¬ 
ply them; either in concentrated solution or dry. Acetic acid is 
supposed to be glacial, and if only a weaker solution is available 
account must be taken of the water in it. 

Condition of the Sample.—If the sample is an alloy, it should 
be in particles as small as the sawings of a hacksaw. If it is a 
soluble salt it need not be fine, but otherwise non-metallic samples 
should be fine enough to pass an 8 o-mesh screen; that is, So 
wires to the inch. 


GROUP i. 

Classification of Samples 


Method A: 

Case i. 

1. The Sample is a Liquid.—A liquid sample must first be ex¬ 
amined to find out what proportion of solid matter it contains. 
Measure io cc. of it into a porcelain dish and evaporate it to 
dryness on a plate over a Bunsen Burner. Scrape out the resi¬ 
due and weigh it. Calculate the volume of the original solution 
that must be taken to contain one gram of solids. 

2. Measure the volume that will contain one gram of solids 
into a 150 cc. beaker and dilute it to 100 cc. with hot water. In 
any case take no more than 100 cc. If a precipitate forms when 
water is added, the sample cannot be treated by Method A. 
Measure out a fresh portion without diluting it and treat it by 
Method B. 

Note. In this and all other cases where the volume of the 
solution containing the sample is to be measured, the measure¬ 
ment is by comparison with water measured into a beaker of 
the same size. 

If no precipitate forms on dilution, the next step is to find 
out whether the sample is neutral, acid, or alkaline. Drop in a 


qualitative; analysis 


89 


piece of litmus paper not larger than one square centimeter. 
Red is acid, blue is alkaline, and purple is neutral. On account 
of its clear indication of neutrality litmus paper is preferred for 
these tests. 

3. If the Sample is Neutral.—Add 2 cc. of HNO^, heat the solu¬ 
tion to boiling, add a drop of HC1, and stir well. If no precipitate 
forms the, sample contains no Ag nor Hg'. Mark the beaker 
Group 2 , and proceed as directed under that head. 

If a precipitate forms, add another drop of HC1, and look 
closely to see if fresh precipitation follows it. If it does, stir, 
allow it to settle, and test again. Continue until no more preci¬ 
pitate is formed. Avoid adding too much HC1, as AgCl is sol¬ 
uble in strong acid. 

Prepare a filter large enough to hold the precipitate without 
filling it more than half full, or at least a nine centimeter paper, 
and pour in a little paper pulp to make sure that the precipitate 
does not run through. Filter into a 150 cc. beaker. Remove the 
filtrate and mark it Group 2 , and proceed with it under that 
heading when convenient. 

Put a fresh beaker under the funnel and wash out the preci¬ 
pitation beaker and then wash the filter thoroughly with hot 
water. Receive a few drops of each washing in a clean cover-glass 
which contains a drop of 5 to 10 per cent AgNO s solution. At 
first a precipitate of AgCl will form from the excess HC1 washed 
out of the paper. When the precipitate no longer forms in the 
washings, the HC1, and presumably the other constituents of 
the filtrate, have been washed out of the filter. 

Note. If the previous precipitation and washing have been 
performed without allowing the solution to cool, any Pb that 
may be in the sample will remain in solution, and will be found 
in Group 2 . Otherwise some of it may be found in the hot 
water washings. 

4 . The precipitate insoluble in hot water may be either AgCl 
or HgCl. Remove the washings and put a clean beaker under 
the filter. Pour NH*OH into the filter and see if any of the 
precipitate dissolves. Stir the mixture in the filter with a rod, 
being careful not to break the paper. AgCl will dissolve in 


90 


NOTES ON CHEMICAL ANALYSIS 


NH 4 OH. HgCl will not dissolve, but will turn black, from re¬ 
duction to metallic Hg. Both may be present. To confirm the 
presence of Ag, dilute the NH 4 OH filtrate to double the volume, 
put in a piece of litmus paper, and add HNO s slowly with stir¬ 
ring until the solution is acid. If Ag is present, AgCl will pre¬ 
cipitate. 

AgCl will turn first purple and then black on exposure to 
daylight. 

5 . If the Liquid is Acid.—It is necessary to find out how much 
acid it contains. Add NH 4 OH a few drops at a time, with stir¬ 
ring, until the solution is exactly neutral to litmus, and then add 2 
cc. of HN 0 3 in excess. If a precipitate forms which does not dis¬ 
solve in this excess, add 2 cc. more. If then it does not dissolve 
on stirring, take a fresh sample and use Method B, as Method A 
is suitable only for low acidity. 

If the sample proves to be suitable for Method A, heat the 
solution to boiling and make the HC 1 precipitation and separa¬ 
tion as directed for the neutral solution, (3), reserving the fil¬ 
trate for Group 2. 

6. If the Liquid is Alkaline.—Add HN 0 3 a little at a time with 
stirring until the solution is neutral, and then 2 cc. more. If a 
precipitate forms when the solution becomes neutral or acid, it 
may or may not be AgCl, but not HgCl, as Hg' would not be 
present in an alkaline solution. If the precipitate appears dif¬ 
ferent, either in color or form, from a freshly prepared AgCl 
precipitate, it will not be convenient to use Method A. A fresh 
portion should be measured out, neutralized with HC 1 , and treated 
by Method B. 

If no precipitate appears when the solution is made acid, or 
if it appears to be AgCl, heat the solution to boiling and add 
HC 1 as directed for the neutral sample, (3), continue the separa¬ 
tion and reserve the filtrate for Group 2. 

Case 2\ 

7 . The Sample is Solid, but Soluble in Water.—Weigh one gram 
into a 150 cc. beaker and add 100 cc. of hot water. 

If the Solution is Acid or Neutral.—Add 2 cc. of HNO s and 
proceed as directed for the neutral sample, (3). Many salts will 


QUALITATIVE ANALYSIS 


91 


dissolve but by hydrolysis form a slight precipitate. If such a 
precipitate remains after adding 2 cc. of HNO s , add 2 cc. more 
and stir well. If the solution clears, proceed by (3). If it does 
not, treat a fresh portion by Method B. 

If the Solid Dissolves to an Alkaline Solution.—Treat the solu¬ 
tion by (6), using Method B if necessary. 

Case 3: 

8 . The Sample is Solid and Insoluble in Water.—Grind the 
sample fine and weigh three portions of 0.5 gram each into 150 
cc. beakers, three different tests being carried on as much as 
possible together, until it is decided which of them is most con¬ 
venient. 

Method B: 

9 . For Alloys and Salts, but not for Ores.—Alloy mixture. Mix 
200 cc. of H 2 0 , 150 cc. of HC 1 , and 20 cc. of HNO s . 

The use of this mixture cannot be reduced to a rule, as some 
substances will not dissolve in it, but it is well suited to some 
others, particularly lead alloys, which are hard to dissolve com¬ 
pletely. 

Try adding 25 cc. of the mixture to one portion of the sample 
and boil slowly for about fifteen minutes. If it dissolves partly, 
continue the boiling, adding more mixture from time to time to 
keep the volume to 25 cc. If the sample does not dissolve com¬ 
pletely in an hour, do not use the method. If the solution is 
complete, raise the cover slightly by hanging a glass hook on the 
side of the beaker away from the lip and boil the solution down 
to about 10 cc., or a little more if crystals cause bumping. Add 
10 cc. more of HC 1 and continue the boiling to 10 cc. again. Add 
a second 10 cc. of HC 1 and boil down again. This is to remove 
HN 0 3 . Add double the volume of hot water, stir well and set 
it away to cool, preferably over night. 

If much Pb is present, a curdy precipitate of PbCl 2 will form 
during the boiling, or on adding the water. PbCl 2 may also 
crystallize from the cooling solution as brilliant needle-like 
crystals. The chemist can identify Pb with certainty by the 
appearance of these crystals, after he has become familar with 
them. 


92 


NOTES ON CHEMICAL ANALYSIS 


Ag, if present in quantity, will form AgCl, but a few milli¬ 
grams will remain in solution. Hg will be divalent, and will 
not precipitate. 

After cooling, filter the solution on a small filter and wash it 
once with 5 per cent HC 1 . In order to insure the complete pre¬ 
cipitation of the remaining Pb in Group 2, it is necessary to 
reduce the acidity to 2 per cent. Neutralize the filtrate with 
NH 4 OH, add 2 cc. of HO in excess, and dilute to 100 cc. If 
a precipitate forms which does not dissolve in the required ex¬ 
cess, measure in enough HC 1 to dissolve it, and keep a record of 
the amount. After passing H 2 S to precipitate the bulk of the 
elements which had hydrolysed, enough water can be added to 
dilute the excess HC 1 to 2 per cent and the H 2 S treatment con¬ 
tinued. 

10 . Returning to the PbCl 2 precipitate, put a fresh beaker 
under the filter and wash it four times more with 5 per cent HC 1 . 
“One washing” is a conventional term whose meaning varies 
with the practice of different chemists. In these notes it in¬ 
dicates the amount which is sufficient to remove almost all of a 
colored solution from an empty filter. This will take about 10 
cc. of solution, applied in a jet on the upper edge of the paper, 
directed down into the folds of the paper, mostly on the triple 
side. 

Discard the washings, put a clean beaker under the filter, and 
pour hot water on the precipitate. PbCl 2 will dissolve, leaving 
AgCl. Continue washing with hot water until no more of the 
precipitate dissolves. Mark the solution Pb and reserve it. 
Test the residue on the paper for Ag as in (4). 

Ammonium Acetate Solution.—Pour into a beaker successively 
8 cc. of NH 4 OH, 10 cc. of water, and 7 cc. of glacial HC 2 H 3 0 2 . 
If the acid is weaker than glacial, leave out the water and pour 
the acid into the NH 4 OH until the mixture is acid to litmus. 

11 . Add 25 cc. of the NH 4 C 2 H 3 0 2 solution to the Pb filtrate, 
stir to dissolve any crystals, and add solution of K 2 Cr 2 0 7 . A 
yellow precipitate confirms the presence of Pb. 


QUALITATIVE ANALYSIS 


93 


Method C: 

12 . For Alloys Free from Sn and Sb, and for Sulfide Ores.—Add 
5 cc. of water and 5 cc. of HN 0 3 . Warm on the water-bath 
or on a hot plate at a temperature below boiling for half 
an hour, or until no more red fumes remain in the beaker. 
Then add 20 cc. of water and heat to boiling. Metallic Pb will 
dissolve better in the more dilute acid, so if the sample seems 
to consist mostly of Pb, the acid should be diluted at the start. 
Keep the solution at boiling heat for half an hour if there seems 
to be action, adding more water when necessary to keep the vol¬ 
ume of the solution. If the sample does not dissolve completely, 
or if there is a milky residue, it is evident that the method is not 
suitable. Free S may be disregarded, except to record it as 
evidence of the presence of sulfides. 

If a sandy residue remains from an ore, examine it carefully. 
If it appears to be ordinary sand, it may be so recorded and 
discarded. If it contains colored minerals it may be fused with 
Na 2 0 2 as in (15). 

If the method is satisfactory, filter into a 150 cc. beaker. Dilute 
the solution to 100 cc. with hot water and test for Ag as in (3). 
Hg' will not be present, owing to the oxidizing power of HNO a . 
The solution remaining from the Ag test is reserved for Group 2. 

Method D: 

13 . For Ores, Particularly those Containing Oxides.—To the half¬ 
gram sample add 25 cc. of HC 1 and let it stand on the water- 
bath or a hot plate at a temperature below boiling for half an 
hour. 

Note: Ten cc. of HC 1 is enough except as a test for W. 

It is good practice to let it stand cold over night before heat¬ 
ing, as HC 1 rapidly loses strength on heating. Then add 5 cc. 
of HNO s , boil down to about 5 cc., remove the cover and evap¬ 
orate to dryness without further boiling. Add 10 cc. of water 
and 5 cc. of HC 1 , cover and warm until the soluble portion has 
dissolved. Add 25 cc. more of water, stir and allow it to cool. 

14 . Filter and wash five times with 5 per cent HC 1 . Reserve 
the filtrate for Group 2. Put a fresh beaker under the funnel 
and wash with boiling water to test for Pb as in (11). Treat 

7 


94 


NOTES ON CHEMICAL ANALYSIS 


the residue with NH4OH as in (4) and test for Ag. Use only 
a small part of the NH^OH filtrate for the Ag test. If the 
sample contains W, part of it will be dissolved in HC 1 and re¬ 
precipitated as yellow WO s , insoluble in acid but readily soluble 
in NH 4 OH to a colorless solution. If the presence of W is sus¬ 
pected, part of the NH 4 OH filtrate should be evaporated to dry¬ 
ness in a porcelain dish and ignited. WO s will appear, red when 
hot and yellow when cold, with perhaps a tinge of green from 
reduction. Ag is not likely to be found in the same sample with 
W, but Sn is, and the latter will remain on the filter, insoluble in 
either acid or NH 4 OH. 

15 . Sodium Peroxide Fusion of the Insoluble Residue.—Wash 
the residue from the paper into the beaker and examine it care¬ 
fully. Any of a great variety of minerals may be present, which 
are insoluble in acids. 

Quartz grains, sand, are most common; transparent and color¬ 
less or slightly tinted. Common rock materials, consisting of 
silicates of Ca, Mg, Al, Fe, etc., come next. They are often of 
a greenish color but may be white or black. Many of them form 
flakes or scales, like mica. 

Barytes is normally white and amorphous, but may be dis¬ 
colored. Undecomposed WO s is brown. Cassiterite is gener¬ 
ally colored brown by Fe 2 0 3 . Oxides of other elements such 
as Sb may be white or colored. 

All of these are fusible in alkalies, and all of the materials are 
made soluble except Ba, which changes to insoluble BaCO s on 
leaching a carbonate fusion in water, but which reverts to in¬ 
soluble BaS 0 4 if the solution is acidulated while the S 0 3 from 
which the fusion separated it is still present. Si 0 2 in small 
quantities will be completely dissolved and will remain in solu¬ 
tion in both the alkaline and acid solutions, until the latter has 
been concentrated by evaporation. 

Record the appearance of the residue for comparison with 
its analysis. Return it to the filter, put it in a nickel crucible and 
burn off the paper. Add from two to five grams of Na 2 0 2 , ac¬ 
cording to the size of the residue, using five if the sample is 
almost all insoluble. Fuse over a Meker burner, holding the 


qualitative; analysis 


95 


crucible in tongs and rotating it obliquely to hasten the fusion. 
Allow the crucible to cool, put it into a 250 cc. beaker, add 100 
cc. of water, leach out the crucible and remove it. Add 2 cc. 
of 1 :i H2SO4 and just enough HC 1 to dissolve the precipitate 
of hydrates. Allow the solution to settle and decant into an¬ 
other beaker, marking it Group 2R. Examine the residue. 
There will be some black scales from the crucible, which should 
be disregarded. If the sample contains Ba, it will be found in 
this residue as white amorphous BaS 0 4 . Sr may also be present, 
with the same appearance. If this white residue is found, dis¬ 
solve the crucible scales away from it with 20 per cent HC 1 , 
dilute, filter, ignite, fuse with Na 2 C 0 3 in platinum or nickel, 
leach with water, filter, dissolve the residue in a little HC 1 and 
test the solution in the flame for Ba and Sr. 

GROUP 2 

17 . The object of the preceding operations is to get the sample 
into condition for the H 2 S precipitation. Incidentally some ele¬ 
ments, Si 0 2 , Ag, Hg', Pb, W, Ba and Sr may have been iden¬ 
tified, though traces of any of them except W and Ba may remain 
undiscovered in solution. 

The elements which may be found in Group 2 are As, Sb, Sn, 
Se, Te, Mo, Ag, Hg, Pb, Cu, Bi and Cd. Note that the first six 
form sulfides soluble in alkalies, while the sulfides of the second 
six are insoluble. As, Sb, and Sn are common and Se, Te, and 
Mo are rare. Pb and Cu are often found in quantity, while Ag, 
Hg, Bi and Cd are either rare or generally found in traces. 

In Chapter III will be found the acid conditions for the H 2 S 
precipitation of most of the elements. Pb requires the lowest 
acidity; not more than 2 per cent HC 1 for certainty of complete 
precipitation. Other elements, such as Sb, if present in large 
quantity, may require a higher aridity than that to keep them in 
solution before precipitation. 

Not more than 5 per cent of free HNO s should be present, 
and H 2 S must not be passed through a hot HNO s solution. If 
both nitric and hydrochloric ions are present, as is the case when 
either acid is mixed with salts of the other, there is danger that 


96 


NOTES ON CHEMICAL ANALYSIS 


the H 2 S will be decomposed and the precipitation fail. This 
danger is increased by heat and high acidity. Therefore it should 
be avoided when possible, and when necessary the solution should 
be kept cold and the acidity should be kept as low as will keep 
the elements in solution before passing the gas, preferably from 
i per cent to 2 per cent. 

HC 1 may be present in any proportion without affecting H 2 S, 
but the greater its concentration the fewer elements will pre¬ 
cipitate. The best strength is just enough to keep all the elements 
in solution. This need never be more than 5 per cent, and pre¬ 
ferably should be from 1 per cent to 2 per cent. 

H 2 S 0 4 may be used mixed with either HC 1 or HNO a without 
affecting the H 2 S precipitation, but the total acidity will be 
greatly increased if it is added to a solution containing nitrates 
or chlorides, owing to its high normal ratio. 

Oxidizing agents such as H 2 0 2 or reducing agents such as 
H 2 S 0 3 must not be present during the H 2 S precipitation, as they 
will decompose H 2 S. 

18 . There may be two solutions for the H 2 S precipitation, 2 
and 2R, which must be kept separate because 2R contains some 
of the crucible, and 2 has to be tested for that element. Regulate 
the acidity of 2 if necessary for complete Pb precipitation, and 
pass H 2 S into both until precipitation appears to be complete. 
If 2 is too strong for Pb on account of other elements, pass 
the gas until the other elements are precipitated and then add 
enough water to dilute the acidity (HC 1 ) to 2 per cent and pass 
the gas again. The collecting and easy settling of the precipitate 
is an indication of complete precipitation. If in doubt, filter a 
little of the solution and pass the gas into the filtrate. 

19 . Prepare a filter amply large for each precipitate, so that 
it may spread in a thin layer and not form a lump. A little 
pulp will help to keep the precipitate from running through. 
Filter and wash the precipitates once, remove the filtrates, mark 
them 3 and 3R, and boil them. In the meantime wash the pre¬ 
cipitates thoroughly, by decantation if they are large enough to 
form a level surface across the filter, with water containing 1 
per cent HC 1 and some H 2 S. Test the washings by letting them 


qualitative: analysis 


97 


run into an excess of NH 4 OH until they no longer show the 
presence of the lower groups by darkening the solution. Wash 
the beaker at first and the precipitate at last, with water, to 
remove most of the acid. 

20 . Removing As and Mo.—In the meantime watch the boiling 
filtrates 3 and 3R to see if any precipitate forms. 

If pentavalent As is present in quantity it will not all be 
precipitated at first, and some will separate by reduction on 
boiling the filtrate. If it appears, distinguished by its being 
yellow while the finely divided S which always separates is white, 
pass more H 2 S, filter on a separate filter, and boil the solution 
again. If more As separates, the operation will have to be re¬ 
peated until it is all removed. The H 2 S should be passed for at 
least fifteen minutes each time. 

Mo also is likely to be incompletely precipitated, and the fil¬ 
trate may be colored deep blue by it, perhaps modified to green 
by other elements, and a brown precipitate may form on boiling. 
The incomplete precipitation is due to reduction, and the Mo has 
to be reoxidized before it can be completely precipitated. This 
is done by oxidizing the Fe as in (21). Before passing H 2 S 
again the acidity must be reduced to 1 per cent and the solution 
cooled. It may be necessary to repeat the oxidation of the fil¬ 
trate to remove a large quantity of Mo. 

Often, when Mo is present, it is the only element to be tested 
for. The regular assay method is then preferable. 3 * 

Test for H 2 S.—Hold a piece of paper moistened with solution 
of Pb(C 2 H 3 0 2 ) 2 in the steam from the beaker. If H 2 S is present 
the paper will be darkened. 

21 . Oxidation of Fe.—All H 2 S should first be boiled out. Allow 
the solution to cool slightly, add a slight excess of KC 10 3 over 
the most Fe that might be in the sample, and boil for a few 
minutes. KC 10 3 will oxidize more than double its weight of Fe, 
in dilute acid. Aqua regia may be used, but it is less reliable. 
The oxidation need not be made if the next group separation is 
to be made by NH 4 SH. 

3 * Holliday and Smoot, cf. Scott, “Standard Methods.” 


9 8 


NOTES ON CHEMICAL ANALYSIS 


22 . Division of the H 2 S Group.—There are now from one to 
three precipitates, 2, and 2R and the recovered As or Mo. If 
the third precipitate is yellow, dispose of it by pouring NH 4 OH 
on the filter. If it dissolves it is As 2 S 3 . Record the fact and 
discard the filter and filtrate. If the precipitate is brown, it 
should be reserved. Mo will probably be found in precipitate 2. 
In case of doubt a fresh sample should be tested by the assay 
method. (See page 97). 

2R will contain, generally, all the Sn from an ore treated 
by Method D, (15). It may also contain Sb, but not much else. 
2 may contain any of the elements of the group. It will be more 
convenient to treat the two precipitates separately, combining the 
solutions afterward. They will be spoken of as one, and in 
most cases there will be but one. 

23 . Stock Alkali Solution.—Weigh about 15 grams of stick 
KOH in a 400 cc. beaker. The amount may be more or less, 
as it is not easy to break off an exactly even weight, so weigh 
what is put into the beaker, add an equal weight of K 2 S 0 4 , and 
add hot water equal to ten times the combined weights, giving 
a solution containing 5 per cent of each reagent. Pass H 2V S into 
the solution for a few minutes to precipitate impurities. Let it 
stand over night or as long as possible before use. Decant the 
clear solution for use. 

24 . With the tube, a spatula or knife blade, assisted by not 
more than 20 cc. of water from the wash-bottle, transfer as 
much as possible of the precipitate to the beaker. Set the beaker 
under the funnel and pour stock alkali through the filter. If 
the precipitate is small, use 25 cc. If it is large, use 50 cc. 
Wash the paper once with hot water. Stir the mixture in the 
beaker to break up the lumps. Heat it almost to boiling, stir 
again and with pieces of paper wet with the solution and held by 
the tube rub down the sides of the beaker, so that every part of 
the precipitate has a chance to dissolve if it will. Heat again, 
fifteen minutes in all, and filter on a fresh paper suited to the 
size of the residue now insoluble. If the treatment has been 
successful, the residue will be perfectly black and will have 
no lumps, filtration will be rapid and the filtrate will be clear 


qualitative: analysis 


99 


yellow. Mark the filtrate 2B, being both combined if there are 
two. The residue from 2R, unless large, may be discarded, as 
it will contain only elements present in 2. 

Put a fresh beaker under 2 and wash with hot water until 
acid H 2 S water gives no precipitate in the last washing. 

Failure to effect a separation of the sub-groups may be due 
to: (A) Acid in the precipitate. Add more stock alkali. (B) 
The presence of SnS. Stock alkali will not dissolve it. NH 4 S X 
dissolves it slowly and unsatisfactorily. After filtering away 
the alkali solution, return the residue to the beaker with 50 cc. 
of warm water, and add Na 2 0 2 a little at a time with stirring 
until the precipitate turns black. It may dissolve completely. 
Now boil the solution for fifteen minutes, dilute, cool, make 1 
per cent acid and precipitate Group 2 as before. After filtering 
and washing make the same stock alkali separation as before. 
The acid filtrate is discarded and the alkali filtrate combined 
with 2B. 

The residue insoluble in alkali is marked 2A. 

GROUP 2A—Ag, Hg, Pb, Bi, Cu, Cd 

25 . Mercury.—Transfer the residue 2A to the beaker with 20 
cc. of water. Add 5 cc. of HNO s and boil two or three minutes. 
All but Hg and some free S will dissolve. Filter while boiling 
hot and wash with hot water into a 150 cc. beaker. Mark the 
filtrate Pb. 

Transfer the black residue to a test tube, add 5 cc. of HC 1 and 
five drops of HN 0 3 , and boil. Pour the solution away from the 
S into a small beaker, add 10 cc. of water and a few drops of a 
concentrated solution of SnCl 2 . If Hg is present, HgCl will 
precipitate, white at first and then turning grey and black through 
reduction to metal. 

Note. If no HgS is present, the S residue is likely to be 
colored by some occluded sulfides of Cu or Bi. A small black 
residue, therefore, is no evidence of Hg, without a further test. 
Notice whether the size of the residue'corresponds to the Hg 
found, to make sure that the other elements were dissolved in 
the dilute HN 0 3 . 


IOO 


NOTES ON CHEMICAL ANALYSIS 


26 . Lead.—To the HNO s filtrate add 5 cc. of H a S 0 4 , cover 
the beaker and boil down to fumes of S 0 3 . Cool, add 35 cc. of 
water, mix well, boil and cool. Pb, if present, will form a heavy 
white precipitate of PbS 0 4 , almost insoluble in dilute H 2 S 0 4 . 
If much Bi is present, some of it will be occluded by the Pb, and 
for a quantitative separation the precipitate should be given a 
special treatment, but the qualitative reactions will not be ob¬ 
scured by the occlusion. Filter and wash with cold distilled 
water. Mark the filtrate Ag. 

Wash the precipitate back with hot water and dissolve it in a 
slight excess of NH 4 C 2 H 3 0 2 . Precipitate PbCr 0 4 as in (11). 

Note. In case of doubt whether Bi is included in the PbS 0 4 , 
add NH 4 OH in excess to the NH 4 C 2 H 3 0 2 solution. Bi will 
precipitate at once, Pb only slowly. By filtering quickly a rough 
separation is possible. The filtrate can then be made acid with 
HC 2 H 3 0 2 and PbCr 0 4 precipitated. 

27 . Silver.—Add a drop of HC 1 to the filtrate from PbS 0 4 . 
Some Ag may have failed to separate by the Group 1 treatment, 
and it will be found here. Remove it by filtration and identify it 
by (4). Mark the filtrate Bi. 

28 . Bismuth.—To the filtrate add NH 4 OH in slight excess. If 
a precipitate forms filter it and mark the filtrate Cu. If no pre¬ 
cipitate forms, there may still be a trace of Bi which NH 4 OH 
will not precipitate. Make the solution slightly acid and add a 
piece of solid ammonium carbonate, enough to make the solution 
alkaline before it entirely dissolves. Boil and set away to cool. 
Filter. 

Sodium Stannite.—Prepare a few cc. of 25 to 50 per cent NaOH 
solution. Pour this into a small volume of SnCl 2 solution with 
stirring, until the precipitate which first forms has dissolved. 
This solution must be concentrated or it will not give the reaction 
for Bi, and it must be fresh, though it may be kept bottled tightly 
for a few days. 

Pour a few drops of the Na 2 Sn 0 2 solution on the precipitate 
supposed to be Bi. If Bi is present, it will turn black through 
reduction to metal. Other elements may be present, but they 
will not turn black. Sn or Sb may not have been entirely sep- 


QUALITATIVE ANALYSIS 


IOI 


arated, and they will appear at this point. Cd may not dissolve 
entirely in the carbonate solution. Therefore, if a precipitate 
of considerable size is formed by carbonate and not by NH 4 OH, 
it should be scraped from the filter and tested for Cd, and only 
a small part tested separately for Bi. In practice Bi and Cd do 
not interfere, because they hardly ever occur in the same sub¬ 
stance. 

Water Precipitation of Bi.—Dissolve the precipitate in a little 
25 per cent HN 0 3 and evaporate it to dryness. If it is very small, 
add five drops of HN 0 3 and 1 cc. of water, and 0.1 gram of 
NH^Cl. Warm until it dissolves and then pour in 100 cc. of hot 
water. For a large precipitate these proportions may be multi¬ 
plied five times. Bi is precipitated as BiOCl, a white crystalline 
precipitate which forms shining waves when gently stirred, the 
“Watered Silk Effect.” This is conclusive evidence of the pres¬ 
ence of Bi, and a better way of estimating the quantity than the 
stannite test. 

29 . Copper.—The filtrate from the NH 4 OH or (NH 4 ) 2 C 0 8 
precipitation of Bi will be colored blue if Cu is present. This 
is a conclusive test if Ni has been completely separated by H 2 S in 
the acid solution. In case of doubt a smaller amount of Cu may 
be identified by immersing a piece of bright Fe in the solution 
over night, after making it acid with H 2 S 0 4 and a few drops of 
HNO s . Cu will plate on the Fe with characteristic color at first, 
turning darker red and dropping off on standing. 

30 . Cadmium.—If Cu has been identified by the NH 4 OH color, 
add solution of NaCN until the blue color disappears, and a 
slight excess. Pass H 2 S. Cd will precipitate as canary yellow 
sulfide. The filtrate from the BiOCl precipitation by water may 
also contain Cd. Pass H 2 S through it. In the acid solution, 
unless the acid is very dilute, CdS has an orange color. 

If Fe has been used to identify Cu, it must be oxidized, pre¬ 
cipitated with NH 4 OH and filtered, the Cd being obtained in the 
NH 4 OH filtrate as before . 

31 . Separation of As, Sb, Sn, Se, Te, and Mo.—If Mo is present, 
it will have been noticed during the previous precipitations, by 


102 


NOTES ON CHEMICAL ANALYSIS 


its incomplete precipitation in acid, and the blue color given to 
the filtrate by the reduced pentavalent Mo. The brown color of 
the precipitate afterward obtained is confirmatory. If these in¬ 
dications appear, it will be necessary to separate it before the 
other elements can be separated from each other. 

If Mo is present, add Na 2 C> 2 to the alkaline solution 2B until 
the solution becomes colorless, and then boil for fifteen minutes. 
Make acid with H 2 S 0 4 . Do this cautiously, to see if any sul¬ 
fides appear when the solution changes to the acid side. If they 
do, the solution must be made alkaline again by the addition of 
Na 2 0 2 and boiled fifteen minutes. To the acid solution add Fe 2 - 
(S 0 4 ) 3 in large excess over the Sn, Sb, etc., not counting the 
Mo, as indicated by the behavior of the original H 2 S precipitate. 
Add NH 4 OH in excess and filter, washing a few times with 
dilute NH 4 OH. Saturate the filtrate with H 2 S. In the presence 
of much Mo the solution will be red instead of yellow. Add 
acid in excess. MoS 3 will precipitate completely, chocolate 
brown. If a large precipitate appears, dissolve the Fe(OH) 3 
precipitate which contains the other elements, in H 2 S 0 4 , pre¬ 
cipitate again with NH 4 OH and test the filtrate for Mo. When 
the Mo has all been removed by repeated precipitations, dissolve 
the Fe(OH) 3 . again in H 2 S 0 4 , adding a little HC 1 if necessary 
for complete solution and precipitate As, Sb, Sn, Se, and Te 
with H 2 S, filter them and wash thoroughly to remove the large 
amount of Fe, and proceed as in (32). Fortunately when Mo 
is found in minerals the other elements of the group are generally 
present only in traces, and qualitatively are hardly worth deter¬ 
mining. The separations in (32) are in most cases made with¬ 
out considering the presence of Mo. 

32 . Add H 2 S 0 4 in excess to the alkaline sulfide solution 2B, 
precipitating the sulfides. Filter and wash free from Cl with 
1 per cent H 2 S 0 4 . Wash back the precipitate and add from two 
to five grams of ammonium carbamate, which dissolves to 
(NH 4 ) 2 C 0 3 . Stir to dissolve the salt and filter. Wash with 
water, twice. Acidulate the filtrate to precipitate As 3 S 3 . The 
other elements remain undissolved in (NH 4 ) 2 C 0 3 . 


QUALITATIVE ANALYSIS 


103 


Wash back the precipitate of the other elements and dissolve 
them by adding Na 2 0 2 with stirring. Boil fifteen minutes. Dilute 
to 100 cc. with hot water. Add H 2 C 2 0 4 .2 H 2 0 until litmus 
paper is colored red, and two or three grams in excess. Stir 
to dissolve and pass H 2 S. All the elements but Sn will preci¬ 
pitate. Filter and wash with 1 per cent H 2 S 0 4 containing no 
H 2 S, making the last washing of beaker and filter with water. 
Mark the precipitate Sb and reserve it. 

If there is much Sn, it will be convenient to make the H 2 C 2 0 4 
filtrate alkaline with NH 4 OH and then acid with HC 2 H s 0 2 . 
SnS 2 will precipitate white, turning to its characteristic brownish 
yellow on standing. Traces of Sn may not be found by this 
method. A more certain way is to add 10 cc. of H 2 S 0 4 to the 
solution, evaporate it to fumes, take up with water, adding 5 
cc. of HC 1 if necessary to bring all but Si 0 2 into solution, add 
dilute KMn 0 4 solution to a pink to make sure that all H 2 C 2 0 4 
has been destroyed, filter from Si 0 2 , dilute to 200 cc. and pass 
H 2 S. This, if all washings have been saved in the previous solu¬ 
tions of Sn, is an accurate quantitative method for small amounts 
of Sn, which can be ignited and weighed as SnO z . 

33. Separation of Se and Te.—Dissolve the Sb precipitate in 
Na 4 0 2 as before, boil, add enough HC 1 to make the solution 
slightly over 30 per cent acid in excess, boil, and pass S 0 2 gas 
for a few minutes. Warm for an hour, if no precipitate forms 
before that time. If a black granular precipitate forms, either 
Se or Te are present. Filter them and mark the filtrate Sb. 
To distinguish between Se and Te, dissolve the precipitates in 
Na 2 0 2 , boil, add 10 per cent excess of HC 1 , boil, add enough 
HC 1 to make the solution 80 per cent and pass S 0 2 . Heat the 
solution to boiling and let it stand cold over night. Only Se 
will precipitate. Filter, dilute the filtrate with four times its 
volume of water, and repeat the S 0 2 treatment. Te will pre¬ 
cipitate. 

The solution containing Sb is diluted to an acidity of not more 
than 10 per cent. H 2 S will then precipitate Sb 2 S 3 , red with a 
suggestion of orange. 


104 


NOTES ON CHEMICAL ANALYSIS 


GROUP 3 

This group includes the elements in the filtrate from Group 2 
which are precipitated by NH 4 OH, Al, Fe, Cr, U, Ti; and to 
this we add V, because it is precipitated by U and partly 
occluded by Fe(OH) 3 ,, though by itself it is not precipitated by 
NH 4 OH. The two solutions, 3 and 3R, must be kept separate 
in order to test 3 for Ni in the next group. 

34 . After boiling out the H 2 S, oxidize as in (21). Add 
NH 4 OH until a precipitate forms. Notice whether there is any 
indication of Fe(OH) 2 . If unfamiliar with its appearance, pre¬ 
pare some by adding NH 4 OH to a solution of FeS 0 4 . If the 
indication appears, add more aqua regia and boil again. Then 
add NH 4 OH until the solution is barely alkaline, and boil until 
the solution no longer smells decidedly of NH 3 . Allow the 
precipitate to settle, filter and wash with hot water. Mark the 
filtrates 4 and 4R. 

35 . The precipitate will contain all the Fe, Ti, Al, Cr, and U. 
If the U is in excess over V, all V will be precipitated. If U is 
present and Fe is present in quantity, enough V will be included 
10 give a test if it is present. In addition, Mn, Zn, Ni, Co, Mg, 
and Ca may be occluded to some extent. Wash the precipitate 
back, add one gram of Na 2 CO s and one gram of Na 2 0 2 and boil 
for ten minutes. This will dissolve U, V, Al, and Cr: U and V 
because they are soluble in carbonates, Al because it forms soluble 
aluminates with the alkalies, and Cr because it is oxidized to 
hexavalence and forms soluble chromate. 

Filter and wash with hot water. Mark the filtrates Ai and 
AiR. Dissolve the precipitates in HC 1 . If there is a brown 
residue insoluble in dilute acid, put a fresh beaker under the 
funnel and pour H 2 0 2 on the residue. If the residue dissolves 
instantly to a clear solution, Mn is indicated. Pb would behave 
in the same way if it were not completely separated before. 

36 . Basic Acetate Separation.—To the cold solution of the Fe 
precipitate add NH 4 OH in slight excess. Form an estimate of 
the probable weight of the precipitate after ignition; by com¬ 
parison with a known weight of Fe if necessary. For every 
0.1 gram of precipitate there should be about 100 cc. in the final 


QUALITATIVE ANALYSIS 


105 


volume of the solution. Dissolve the precipitate in as little HC 1 
as possible. Add a 5 per cent NH 4 OH solution a few drops at 
a time and finally dropwise, stirring after every drop, until the 
small precipitates formed by the drops of dilute NH 4 OH dis¬ 
solve with difficulty and the solution takes the dark reddish color 
which indicates a neutral solution of Fe. If a permanent pre¬ 
cipitate forms through adding too much NH 4 OH, dissolve it in 
HC 1 and approach neutrality again with the dilute NH 4 OH. 

Then add from two to three grams, according to the amount 
of precipitate, of NaC 2 H 3 0 2 .3 H 2 0 dissolved in hot water, boil 
for one minute, and allow the precipitate to settle without getting 
cool. If there is any delay, keep the beaker on the water-bath. 
Prepare a rapid filter, amply large. For 200 cc., use eleven centi¬ 
meters; for 300 to 400, use twelve and one-half centimeters. 
When the precipitate has settled, except a few flakes which may 
persist in floating about, take up the beaker in tongs or with a 
cloth, remove the rod carefully so as not to stir up the precipi¬ 
tate, and pour the clear solution through the filter without set¬ 
ting the beaker down. If the filtrate becomes slow before the 
beaker is empty, keep the solution hot on the water-bath until it 
has all been transferred to the filter. Wash out the beaker 
with boiling hot water as soon as there is room in the filter for 
the washings, and as soon as the level has fallen one centimeter 
from the top, wash around the top. Wash twice more after the 
filter has drained completely. 

Fe and Ti are precipitated, with any A 1 that was not dis¬ 
solved by the alkaline solution, free from Mn, Zn, Ni, Co, Ca, 
and Mg. If Cr were absent, this separation could be used in 
place of the NH 4 OH precipitation, but trivalent Cr is incom¬ 
pletely precipitated in presence of HC 2 H 3 0 2 . Mark the filtrates 
4 and 4R, concentrate them by boiling, and add them to the 
other Group 4 solutions. 

In this precipitate Fe can be recognized by its color without 
any other test. If only a trace appears, it may come entirely 
from impurities in the reagents, and a conclusive test requires 
a quantitative comparison between the sample and a blank de- 


io6 


NOTES ON CHEMICAL ANALYSIS 


termination on the same quantities of reagents as are used with 
the sample. 

Wash back the Fe precipitates, add 9 cc. of HNO s and stir 
to dissolve. Add a little Na 2 0 2 . A yellow color, more intense 
than that of Fe, running to orange when the element is present 
in quantity, indicates Ti. A cherry red indicates V. The V 
may hide Ti. In such a case, divide the solution into halves and 
add HF to one half. This will bleach the Ti color, and by 
comparison of the two it can be seen whether both are present. 
If the division has been made, discard the half to which HF has 
been added, and to the other half add between 3 and 4 cc. of 
NH 4 OH. If no division has been made add between 7 and 8 
cc. Stir to complete solution. Add KMn 0 4 to a pink and then 
FeS 0 4 solution to bleach the pink. Add 10 or 20 cc. of reagent 
ammonium molybdate. A yellowing of the solution indicates P. 
A precipitate will form on stirring for ten minutes. The pre¬ 
cipitate is 1.63 per cent P. 

37 . Precipitation of A 1 from Carbonate Solution.—To the car¬ 
bonate solutions marked Ai and AiR add 20 per cent HNO* 
until all of the normal carbonate has been changed to bicarbon¬ 
ate. This is shown by testing with turmeric paper until after 
successive additions of 1 cc. of acid the paper is no longer 
reddened by a drop of the solution. The change of litmus 
paper to purple is also an indication, but turmeric is easier to 
read. If Al is present in quantity it will precipitate before neu¬ 
trality is reached. The precipitate is colorless and gelatinous. 
The certainty of this test depends on the completeness of previ¬ 
ous separations, and assumes the absence of rare elements such 
as Ga, but for most purposes it is sufficient. 

Allow the precipitate to settle and filter, marking the solu¬ 
tions U and U R. Al in the R portion is an indication of clay 
or feldspar in the gangue. Some of the P 2 0 5 may have dis¬ 
solved in the alkaline solution. If a fusion had been made of 
the NH 4 OH precipitate with Na 2 CO s or Na 2 0 2 all the P would 
be found in solution and would be precipitated as A 1 P 0 4 . Dis¬ 
solve the precipitate in 9 cc. of HNQ 3 , add 7 cc. of NH 4 OH, 


QUALITATIVE ANALYSIS 


107 


dilute to 100 cc. with warm water and precipitate P with 20 
cc. of ammonium molybdate solution. 

38 . Uranium and Vanadium.—To the filtrates U and UR add 
HNO s in excess, boil out the C 0 2 and add NH 4 OH in excess. 
If U is present it will be precipitated as yellow (NH 4 ) 2 U 2 O t . 
If V is also present it will be precipitated with U. Filter and 
mark the filtrates Cr and CrR. Dissolve the precipitate in 
HN 0 3 and test the solution with H 2 0 2 for V. 

Note. U will always be found in the soluble, and hardly ever 
in the residue insoluble in acid. V from the U mineral Car- 
notite is also soluble, but Roscoelite, containing no U contains 
insoluble V. Cr is more likely to be found in the R portion. 

39 . Chromium.—If Cr is present the solution will be yellow or 
orange. Add a few drops of H 2 0 2 . Cr in quantity will give a 
momentary blue, fading to pale green or rose color. If V is pres¬ 
ent, it will show red. Add H 2 S 0 3 to decompose excess H 2 0 2 , 
then NH 4 OH in excess, and boil. Cr will yield an apple green 
precipitate of Cr(OH) 3 . The filtrate may be further tested 
for V. 

GROUP 4 

40 . Manganese.—Reserve solution 4R, add NH 4 OH and 
(NH 4 ) 2 S 2 O s to solution 4 and boil. Mn, if present will produce 
a brown precipitate approximating MnO z . Filter and wash with 
hot water. Treat the precipitate with 10 per cent H 2 S 0 4 and 
then with H 2 0 2 . If it remains insoluble in the acid and dis¬ 
solves instantly in H 2 0 2 , the presence of Mn is confirmed. 

41 . Ammonium Sulfide Precipitate.—Make 4R slightly alkaline 
and pass H 2 S into it and the filtrate from Mn. 4R will give a 
large precipitate of NiS, which must be discarded. Zn, if alone 
in 4, will form white ZnS. Ni or Co will make the precipitate 
black. Filter and wash with NH 4 SH, and boil the filtrates. If 
a black precipitate forms, filter again and wash with NH 4 C 1 
solution. Mark the filtrates 5 and 5R, add HC 1 and boil out 
the H 2 S. 

42 . Separation of Zinc from Nickel and Cobalt.—Put both papers 
and precipitates from 4 one beaker, discarding those from 
4 R. Add 10 cc. of HNO s and 10 cc. of H 2 SQ 4 . Boil down to 


io8 


NOTES ON CHEMICAL ANALYSIS 


fumes of SO s and add a few drops of HN 0 3 at a time until the 
black residue of carbonaceous matter is destroyed. Cool, dilute, 
neutralize with NH 4 OH and make acid not more than 0.2 per 
cent with H 2 S 0 4 . Pass H 2 S briskly. ZnS alone will precipitate. 
Filter, add NaC 2 H 3 0 2 to the filtrate, and pass H 2 S, which will 
precipitate Ni and Co. Filter, wash the precipitate back, add 
HN 0 3 and boil until the precipitate is dissolved. Evaporate the 
solution to dryness. A green crystalline residue indicates Ni. 
A rose-colored deposit indicates Co. If both are present, they 
can be seen separately in different parts of the beaker. When 
one is seen clearly a precipitation test may be made for the other. 

43 . Nickel in Presence of Cobalt.—Take up the residue in water, 
add HC 1 and alcoholic solution of di-methyl glyoxime, and then 
NH 4 OH to neutrality. A rose red precipitate confirms the pres¬ 
ence of Ni. 

44 . Cobalt in Presence of Nickel.—Take up with water and HC 1 
and make the solution 15 per cent acid with HC 2 H 3 0 2 . Add 
nitroso beta naphthol, dissolved in 50 per cent HC 2 H 3 0 2 . A 
bright red color, collecting to a red precipitate on standing, indi¬ 
cates Co. The reagent may produce a brown precipitate which 
does not contain Co. 

GROUP 5 

45 . There may be two solutions, kept separate for the purpose 
of showing whether the Ca and Mg in the sample are there as 
silicates or as salts soluble in acid. Add NH 4 OH in excess, 
boil and add to the boiling solution of about one gram of 
(NH 4 ) 2 C 2 0 4 .H 2 0 . Ca will precipitate, with Sr. Filter, dis¬ 
solve the precipitate in HC 1 and test in the flame for Ca and Sr. 

46 . Cool the filtrates from Ca, add a solution of a phosphate 
and stir. If a precipitate does not form within a few minutes, 
add NH 4 OH to 10 per cent of the volume and stir again. A 
precipitate may collect on standing over night. MgNH 4 P 0 4 .- 
6 H 2 0 is a white semi-transparent crystalline precipitate. It 
may appear on lines rubbed by the rod in stirring. 

47 . Barium is properly a member of this group, but on account 
of the insolubility of the sulfate it is separated in the beginning 
of the analysis. 


qualitative: analysis 


109 


GROUP 6 

48 . Sodium, Potassium and Lithium.—On account of the large 
mass of salts accumulated in the analysis it is inconvenient to 
separate Li and K, and impossible to identify Na, as salts of Na 
have been added. It is customary to test for these elements by 
regular quantitative procedure, based on the method of J. 
Lawrence Smith. Salts of these elements are easily identified by 
their distinctive flame tests. In the case of Na the test is so deli¬ 
cate that it is seen in almost any substance. Na in quantity is 
distinguished when a yellow of great intensity is produced by a 
minute amount of the sample, under conditions that did not yield 
such a color before the sample was added. 


8 


CHAPTER VII 

DETERMINATIONS 

Arsenic.—As is obtained in HC 1 solution as AsC 1 3 by the Fischer 
distillation method. In small quantities up to one-tenth gram 
it is weighed as As 2 S 3 . In larger quantities, particularly when 
obtained from materials free from Sb, which may contaminate 
the distillate, it is titrated with iodine solution. 

Weighing as As 2 S 3 .—If there is a possibility of Sb being pres¬ 
ent, make sure that the solution is at least 60 per cent HC 1 . Pass 
H 2 S, and allow the solution to stand until the precipitate has 
settled. The best condition for filtering is when the precipitate is 
in loose flakes, not settled to a solid layer. In this condition 
policing is easier. 

Prepare a rapid Gooch filter, and without drying pour in the 
solution, pushing the floating precipitate back so that it does not 
get into the crucible until toward the end of the filtration. Wash 
out the beaker and police with a earners hair brush, as the pre¬ 
cipitate sticks to rubber. Wash down the sides of the crucible 
once, remove it and wipe the outside, and lay it on its side in a 
shallow tray, such as a filter box, and dry it at ick>° for thirty 
minutes. Allow it to cool in the open air until the crucible feels 
cold when touched to the forearm, and weigh. 

Dissolve the As 2 S 3 by passing NH 4 OH through the crucible, 
dry as before, and weigh, taking the weight of the precipitate by 
loss. If there is free S precipitated with the As 2 S 3 , a little of 
it will dissolve in the ammonia, giving high results. Generally 
this error is less than the losses of As during the distillation, 
and may be neglected. It is possible to dissolve the S away from 
the As 2 S 3 by CS 2 , but the precipitate must be perfectly dr^. 
Some chemists wash out the water with alcohol, and the alcohol 
with ether before applying the CS 2 , but in the writer’s experience 
this does not get the precipitate sufficiently dry to allow the CS 2 
to act perfectly. It is better to dry in the oven, then treat the 
precipitate with CS 2 , wash it out with ether, and dry again be¬ 
fore weighing. The crucible may be weighed before the filtra¬ 
tion or afterward. It is safer to do it afterward, for then it 
can be seen whether all the free S has been removed. 


DETERMINATIONS 


III 


If some Sb has been precipitated with the As, it is possible 
to dissolve the As 2 S 3 away from it by using a strong solution, 
io per cent or more, of (NH 4 ) 2 CO s , which does not dissolve 
other sulfides than those of arsenic. 

Titration with Iodine.—Iodine solution. Decinormal. 

Starch. Soluble starch, i per cent mixture, boiled and cooled. 

Neutralize the acid in the distillate with NH 4 OH, add a slight 
excess of HC 1 , cool in ice water or running water, add solid 
NaHCO s in excess, so that some remains undissolved for a 
moment after the solution becomes neutral, add 2 cc. of starch 
solution, and run in iodine solution at a regular rate, stirring 
vigorously all the while, until purple appears in the solution. 
Then add the solution dropwise until the blue appears. 

A blank titration with these reagents and no As will give about 
o.i cc. of decinormal iodine. 

A blank obtained by distillation may be large as 0.25 cc. 

The solution should be standardized against pure sublimed 
As 2 0 3 . This is easily prepared by placing some C. P. white 
arsenic in a flat-bottomed crucible in the bottom of a casserole, 
covering the casserole, and putting a Bunsen flame directly under 
the crucible. By a proper adjustment of the flame, the As 2 O s 
will sublime on the sides of the casserole in dense crystals. These 
should be kept in a glass-stoppered bottle or in a dessicator. 
Weigh 0.25 gram of the As 2 0 3 into a large beaker, dissolve it in 
a little concentrated NaOH, dilute to the volume of the neutral¬ 
ized distillate, add HC 1 in slight excess, neutralize with NaHCO, 
and titrate. 

On account of the large end point correction, and also to guard 
against losses in distillation, it is more accurate to distil the 
standard under the same conditions as the sample. The assay 
of a white arsenic is merely obtaining the ratio between the 
figure obtained with it and that from an equal weight of pure 
As 2 0 3 . 

Antimony.—Sb is titrated with decinormal KBrO s , by a modi¬ 
fication of Gyoery’s method described by Low. 4 

* I^ow ‘ Technical Methods of Ore Analysis.” 


112 


NOTES ON CHEMICAL ANALYSIS 


The Sb must be obtained in an HC 1 solution free from HNO g 
or other reducing agents. Cu and Fe may be present only in 
traces. A workable scheme, which permits the presence of as 
much as two grams of Pb or Sn, and a considerable amount of 
alkali salts, is as follows. 

The solution should be brought to a volume of 75 cc. of 50 
per cent HC 1 . If the sample is a suitable alloy, weigh from 
three-tenth to two grams into a 400 cc. beaker, add 75 cc. of HC 1 
and warm on the top of a water-bath or oven at a temperature 
not above 8o° until the evolution of H has ceased. Add 50 cc. 
of warm water. 

Add KClOg a little at a time until free Cl is in excess and the 
precipitated Sb is dissolved. Boil down to 75 cc., and the solu¬ 
tion is ready for the reduction. 

If the sample is in a sulfide solution, evaporate it if necessary 
to 75 cc. of warm solution, add an excess of KC 10 3 and 50 cc. 
of HC 1 , stir until all sulfides are decomposed, and boil down to 
75 cc. 

A sample of pure metallic antimony, or the standard, is 
more easily dissolved by adding 75 cc. of hot water, 50 cc. 
of HC 1 , and excess of KC 10 S , and stirring occasionally to keep 
cakes from forming, until solution is nearly complete, and then 
boiling. 

Reduction of Sb.—To the cold solution, 75 cc. of 50 per cent 
HC 1 , add 40 cc. of H 2 SO s solution of 1.03 specific gravity or 
stronger. Stir well and leave the rod in the beaker. Boil down 
briskly to 75 cc. and cool. Add 20 cc. of the H 2 SO s and 60 cc. 
of HCl r stir, and boil down to 75 cc. again. In the meantime 
boil a mixture of 40 per cent HC 1 , and when the sample has 
reached about 75 cc. add 50 cc. of the 40 per cent HC 1 . A well 
made graduated cylinder can be used safely to measure the hot 
acid. 

Finally boil down to 75 cc., add 100 cc. of boiling water and 
titrate at once. The titration is conducted as follows. 

Decinomial Potassium Bromate.—Methyl orange, one gram per 
liter in water. 


determinations 


113 

Add one drop of methyl orange. Run in the bromate solu¬ 
tion from a burette in a regular stream with vigorous stirring 
until the red shows signs of fading. Add another drop and pro¬ 
ceed until fading is noticed again. Add a third drop and con¬ 
tinue the titration dropwise until the pink entirely disappears. 
One-tenth cc. is about the right subtraction for the end point. 

After a little practice to get accustomed to the rate of fading 
of the methyl orange, this method of titration is rapid and easy. 
Errors are due more to lack of attention to the boiling than to 
any other cause. The chemist is always aided by having seen 
the Sb before titration, either as sulfide or as precipitated metal 
during solution. 

The solution is standardized against an analysed sample of 
metallic antimony. It is difficult to obtain a sample purer than 
99.5 per cent, but the impurities do not interfere with the titra¬ 
tion, needing only to be counted in measuring the Sb present. 

Small amounts of Se and Te precipitated during the reduction 
will dissolve on boiling and do not interfere with the titration. 

As, if reduced, is expelled. If not reduced, it does not inter¬ 
fere, so no attention need be paid to it if the scheme is followed 
exactly. The writer has found as much as 0.12 gram of As after 
an Sb titration, separated it, and afterward obtained the same 
figure for Sb. 

Low says that Fe interferes very little. The writer has found 
that less than 0.003 gram of Fe may be disregarded. More should 
be separated, as it may make large errors. 

The advantage of this method over the many others available 
is mostly in its freedom from the interference of As, Se, and Te. 

Tin.—Sn is weighed as Sn 0 2 or titrated with iodine solution. 

The gravimetric method is useful for the determination of 
amounts of Sn so small that they might be confused with the 
end point correction of a titration, or which have been obtained 
in the course of a qualitative test. 

It can be made part of a nearly complete analysis of an alloy 
on one weighed portion. The details of this method consist princi¬ 
pally in the handling of the other elements which are occluded 


NOTES ON CHEMICAL ANALYSIS 


114 

with Sn in precipitation. The method will therefore be discussed 
under Separations. 

The titration method follows the reaction 
SnCl 2 + 2 HC 1 + 2 I = SnCl 4 + 2 HI. 

Standard solution, decinormal iodine. 

Indicator, 1 per cent starch solution. 

Reducing element, a piece of nickel 0.015" x 2" x 6" made into 
a loose roll, as large as can be put into the flask, through which 
liquid can circulate easily. 

Apparatus, a 500 cc. Erlenmeyer flask with a “sulfree” rubber 
stopper and tube as shown in Fig. 14. The diameter of the out¬ 
let tube should be about 3.5 millimeters and the capacity about 



12 cc. to insure quiet action of the carbonate solution. This form 
of outlet tube was suggested by Charles G. Snyder, who used 
a bent pipette. 

The Sn should be a soluble form free from oxidizing agents 
which cannot be boiled out, such as HNO s . Not more than 0.005 


















DETERMINATIONS 


115 

gram of Cu should be present. The effect of Cu is to precipitate 
as metal and dissolve during the titration, giving high results. 
As in the traces usually found in engineering materials does not 
interfere, though in quantity it is said to deposit on the nickel and 
carry some Sn with it. 

The iodine solution is standardized against pure tin. Weigh 
different amounts up to 0.3 gram into flasks, add 15 cc. of H 2 S 0 4 
and heat strongly until solution is complete. Cool, dilute, add 
from 200 to 250 cc. of water and 30 cc. of HC 1 , put in the re¬ 
ducing roll, connect the stopper and tube and heat to boiling. 
Keep it gently boiling for forty-five minutes. Place a small 
beaker containing boiling water and a few grams of NaHC 0 3 on 
the hot plate and insert the end of the outlet tube without stopping 
the boiling.. Make sure that all air is expelled from the tube, re¬ 
move beaker and flask without allowing air to enter, and cool the 
flask in running water or ice water. As soon as the carbonate 
solution has ceased to oscillate, remove the stopper, add 2 cc. of 
starch solution and run in the standard iodine in a regular stream 
with as much stirring as possible by rotating the flask obliquely 
without breaking the surface of the liquid. As the Ni forms a 
green solution, it is of advantage to hold the flask above a well 
illuminated white paper, so that the blue of the starch can be 
seen. When the blue appears the end is near. A purple or pale 
blue that remains after mixing is one drop from the end. 

An end point subtraction of about 0.2 cc. is required. 

Alloys which can be decomposed by H 2 S 0 4 alone, and which 
contain no interfering impurities, such as solder, type metal, etc., 
may be run in the same way as the standard. Instead of H 2 S 0 4 , 
an equivalent of HC 1 , amounting to 65 cc. in all, may be used, 
as in acidulating the solution from a sodium peroxide fusion. 

Lead.—Pb is weighed as PbS 0 4 and PbCr 0 4 . The titration 
methods take almost as much time as the gravimetric, and are 
less accurate. 

Having the Pb in solution, preferably in slightly dilute HNO a , 
add sufficient H 2 S 0 4 to give excess over all bases present; pre¬ 
ferably 10 cc. for a 400 or 600 cc. beaker, and 0.3 gram or more 
of Pb, and 5 cc. or less for smaller beakers and less Pb. The 


Il6 NOTES ON CHEMICAL ANALYSIS 

acid should be enough to cover the bottom of the beaker. Cover 
the beaker and boil down to fumes of SO s . A drop of HNO s 
which hangs on the under side of the lid causes no appreciable 
error. Cool, add from six to eight times as much water as there 
is acid, mix well to prevent explosion, and boil until all soluble 
salts are dissolved. Cool and let stand for thirty minutes or 
more. If no impurities remain insoluble, and the filtrate is not 
needed, the Pb may be weighed as PbS 0 4 . Otherwise it is more 
convenient to convert it to chromate. 

Lead as Sulfate.—Prepare a Gooch crucible filter, dry and 
weigh it. Filter and wash the precipitate with i per cent H 2 S 0 4 , 
transferring all of it to the crucible. Wash out the acid with 
absolute alcohol, dry, heat almost or quite to redness, cool and 
weigh. The theoretical factor is used. 

Lead as Chromate.—Ammonium acetate solution. Mix eighty 
volumes of NH 4 OH, one hundred of water, and seventy of 
glacial acetic acid. Twenty-five cc. of this solution, which fills a 
nine centimeter filter, is enough for 0.5 gram of Pb. Larger 
amounts, particularly if in cakes or flakes instead of grains, may 
require more. 

Potassium Dichromate. Cold Saturated Solution.—The pres¬ 
ence of insoluble Si 0 2 , or a little hydrolysed Sn, may be disre¬ 
garded, as they carry no Pb and remain insoluble in acetate. 

If there is enough Ca, Bi, or Sb to contaminate the sulfate 
precipitate, they will interfere with the chromate determination. 
Such cases will be discussed under Separations. 

Having the PbS 0 4 ready to filter, prepare a small rapid filter 
with a narrow-stemmed funnel. Nine centimeters is generally 
the best size. The corner should be tom off if there is no fine 
residue of pulverized quartz. If there is, the paper should be left 
entire and the column secured by a little pulp poured around the 
edges of the paper. Filter, wash the precipitate into the filter but 
do not police the beaker. Wash the top of the paper free from 
acid, testing by touching the paper with the tongue. 

It is useless to test the filtrate, as water causes the PbS 0 4 to 
hydrolyse, not dissolving Pb but making the washings acid. 


determinations 


II7 

With hot water in the wash-bottle wash back the precipitate, 
holding the filter with the inside flap downward, and folding the 
flap back with a knifeblade to wash under it, so that all of the 
precipitate is removed from the paper. Before washing back 
warm the lower edge of the funnel by playing hot water on it. 
This will keep the precipitate from sticking to it. 

Fill the paper once with the hot acetate solution, adding more 
if the precipitate is large and does not dissolve quickly. If the 
precipitate is fine it will dissolve with stirring only. If it is 
caked or has flakes it should be warmed but not boiled, with 
occasional stirring, until all Pb is dissolved. If anything remains 
which is not recognized as a residue which will not contain Pb, 
such as sand, further work is necessary, which will be discussed 
under Separations. 

When the Pb is all dissolved, filter and wash once with hot 
water, receiving the filtrate in a 400 cc. beaker for 0.5 gram or 
more of Pb and smaller sizes in proportion. 

Pour 2 to 5 cc. of acetic acid into the filter and fill it with 
hot water, so that all of it is washed with the dilute acid. This 
is to dissolve any basic lead acetate which the hot water may 
leave in the paper. Wash three or four times more with hot 
water. Dilute the filtrate to 300 cc. or less in proportion to the 
amount of Pb, with hot water. Add the dichromate solution 
from a pipette with stirring until the color of the solution ob¬ 
scures the pale yellow of the precipitate, making it appear 
slightly orange. Ten cc. is enough for 0.5 gram of Pb, Warm 
on the water-bath with occasional stirring until after stirring the 
precipitate settles quickly, leaving a clear solution. Cool in ice- 
water or let stand over night. 

Prepare a weighed Gooch crucible. Filter the cold solution, 
using the full force of the suction, transfer the precipitate to the 
filter and police the beaker at once. Wash the sides of the cruci¬ 
ble with hot water and flood the precipitate twice. Dry the 
crucible in an oven which heats gradually, reaching 6oo°, or such 
a temperature that parts of it show red, in from fifteen to thirty 
minutes. If no oven is available, place the filter in an ordinary 
crucible over a Bunsen flame and heat gradually until in the 


Il8 NOTES ON CHEMICAL ANALYSIS 

same time the outer crucible shows red in spots. Cool in open 
air and weigh. 

As PbCr 0 4 contains a little water, it is necessary to use an 
empirical factor, somewhat lower than theoretical. The writer 
has found a factor of 0.6381 for the Gooch filter dried at ioo°, 
and 0.6391 when dried at 6oo°. 

Small amounts of PbCr 0 4 may be filtered on paper and 
ignited. If the filter is carefully roasted the error will be in¬ 
appreciable. 

Bismuth.—Bi is weighed as BiOCl. It must be in solution free 
from other acids than HN 0 3 and HC 1 . Small amounts of 
elements which do not easily hydrolyse, such as Pb and Cu, may 
be present, but Sb and more than traces of Fe must be absent. 

Evaporate the solution to dryness. If the residue appears to 
contain only a few milligrams of Bi, add six drops of HN 0 3 
and 2 or 3 cc. of hot water and warm to dissolve. Disre¬ 
gard a small cloudiness. Add about 0.2 gram of NH 4 C 1 and 
warm again. The residue should now dissolve. If it does not, 
further separations are necessary. 

Now add 300 cc. of hot water. Stirring is not necessary. The 
precipitate should form in glancing crystals, giving the “watered 
silk” efifect. Cool, filter on a weighed Gooch crucible, dry at 
ioo° and weigh as BiOCl. The theoretical factor is used for 
small amounts. 

For larger amounts, more than 0.01 gram, the same procedure 
is followed, but all the quantities are increased. For 0.2 gram of 
Bi there should be enough acid to keep a clear solution at 20 cc. 
volume. It is best to add about fifteen drops of HNO s and half a 
gram of NH 4 C 1 and a few cc.’s of hot water, and if a milky pre¬ 
cipitate forms add enough acid to dissolve it, then NH 4 OH un¬ 
til a slight cloudiness forms, and then HNO s drop by drop until 
the solution is clear again. Now add a little more hot water, 
and if no precipitate forms, dilute to 300 cc. 

If there is as much as 0.5 gram of Bi, it should be kept in 
solution up to 50 cc. or more, and then largely diluted. With 
care and good luck a crystalline precipitate can be formed with 
large amounts of Bi, but unless the precipitate is formed at so 


DETERMINATIONS 


119 

great a concentration as to occlude the other elements, the re¬ 
sults will be accurate with a light cloudy precipitate, though 
filtration will not be so easy. 

For large amounts of Bi an empirical factor should be estab¬ 
lished. 

Copper.—The most accurate method for the determination of 
Cu is the electrolytic. The details of the method must be worked 
out by each laboratory to suit its requirements for time and ex¬ 
pense, and its available apparatus and current. Where a few 
determinations are to be made quickly, the rotating anode or 
other stirring device is used. Where economy of labor is im¬ 
portant, it is best to use fixed electrodes with deposition period 
of several hours, preferably over night. 

The best electrolyte is a mixture of HN 0 3 and H 2 S 0 4 . The 
amount of HNO s depends principally on the amount of Cu to 
be deposited. HNO s is converted to NH 4 OH during the elec¬ 
trolysis of a Cu solution. In plating one gram of Cu as much 
as 2.45 cc. of reagent HNO s may be reduced to NH 4 OH. 5 It 
is necessary to have enough HN 0 3 to last through the electroly¬ 
sis, and enough volume of electrolyte to dilute the acid, so that 
the concentration may not prevent deposition. 

The amount of H 2 S 0 4 depends more on the volume of the 
solution and the amount of current, as it is not altered during 
the electrolysis, except to increase through the disappearance of 
the Cu ions. The object of its use is partly to increase the con¬ 
ductivity of the solution and partly to prevent the deposition of 
other elements. 

Nitrites may be present when H 2 S 0 4 is used. When only 
HN 0 3 is used, even the fresh reagent must be boiled before 
electrolysis to free it from HN 0 2 . 

An example of a satisfactory electrolyte is two grams of Cu in 
175 cc. of solution containing 6 cc. excess HNO s and 10 cc. 
H 2 S 0 4 , with a cathode of about 100 square centimeters plating 
surface and 0.5 ampere for twelve to fifteen hours. But there 
are so many factors to be considered that only experiment on a 
particular equipment will show what solutions should be used 

6 Euckow. Zeit. Anal . Chttn., 19 , n, 1880. Easton,/, A. C. S., 25 , 1042. 


120 


NOTES ON CHEMICAL ANALYSIS 


with it. Such books as Smith’s “Electro-Analysis,” and Heath s, 
“Analysis of Copper,” give valuable data and advice. 

The best cathode for slow deposition is a cylinder made of 
perforated sheet platinum. This is easily kept clean by polish¬ 
ing occasionally with a rotating steel bristle brush, so that its 
weight changes very little from day to day. The perforations 
permit the circulation of the solution almost as well as gauze 
under the slight impetus of the bubbles rising from the anode, 
and keep down the tendency to “sprout” or form arborescent 
extensions. 

The best anode is the largest that can be conveniently placed 
inside the cylinder without danger of touching on slight move¬ 
ment. A basket is better than a coil, and a coil is better than 
a straight wire. A helically coiled wire, occupying a cylindrical 
space half the diameter of the cylinder, is good compromise. 
It distributes the current evenly the length of the cathode. 

HC 1 in more than traces prevents the formation of a good 
dense deposit, though it is possible by careful measurement to 
precipitate Ag with dilute NaCl without interfering with the Cu 
deposit from the filtrate. 

Se and Te are as easily deposited as Cu, and must be absent 
or accounted for, to reverse the military phrase. Ag and Bi are 
also deposited with Cu and prevent the formation of a good 
deposit. Sb, As, and Pb in small quantities do not interfere if 
there is a sufficient volume and concentration of H 2 S 0 4 . Sn 
does not interfere except mechanically when there is a large 
precipitate. Fe in large quantities sets up oxidizing reactions 
which prevent deposition. 

Copper by Color.—In small quantities Cu is conveniently de¬ 
termined by color comparison. A standard solution should be 
kept containing one gram of Cu per liter, or one milligram per cc. 
The Cu for comparison is generally obtained as CuS. The pre¬ 
cipitate should be ignited in a small porcelain crucible, prefer¬ 
ably with a flat bottom and vertical sides. The ignited residue 
is dissolved in HNO s , evaporated to a few drops, diluted 
slightly, and NH 4 OH in excess added. A similar crucible is 
used for the standard. NH 4 OH is put into it and the standard 


determinations 


121 


copper solution run in from a burette until the color is matched 
at the same volume as the sample. 

Sometimes a small amount of impurity alters the color of the 
solution to green or purple. A little ferric oxide rouge added 
to the standard will give it the purple cast to match, and a trace 
of K 2 Cr 0 4 will produce the green. It is often impossible to 
make any comparison unless this alteration is made, as the small 
precipitate is likely to be impure. The effect of a white pre¬ 
cipitate or residue is matched by an inert white powder such as 
ground quartz. 

The crucible is the best container for small amounts of Cu 
from o.oooi to 0.002 gram. For larger amounts a comparison 
tube, short and wide enough to stand alone, is convenient. 
This tube should be just large enough to admit the cathode, so 
that small dark deposits may be dissolved and compared with a 
minimum of solution. 

Cadmium.—A good general method for the determination of 
Cd is electrodeposition from a cyanide solution. Zn must be 
absent. Cu, if present, may be determined afterward by color 
and the weight deducted. After the separation of Cd from 
other elements, it is obtained as CdS on a paper filter. The 
paper is destroyed and the Cd dissolved by treatment with 
HN 0 3 and about 5 cc. of H 2 S 0 4 . After destroying the organic 
matter, the cover of the beaker is removed and the free H 2 S 0 4 
expelled. Take up with water, add a gram of NaCN in solution, 
transfer to an electrolysis beaker and electrolyse with a very 
low current, not more than N.D. 100 == 0.1 ampere. The deposition 
is rapid, two hours with fixed electrodes being enough for small 
quantities. 

By careful adjustment of acidity to current, or by the use of 
limited voltage as directed by Smith, 6 Cd may be determined 
in presence of Zn, so that the partial separation of that element 
in the analysis of spelter is enough. For this purpose it is neces¬ 
sary to expel all HN 0 3 and its decomposition compounds by 
repeated evaporations of the H 2 S 0 4 solution to fumes of S 0 3 

• Smith. “Electro-Analysis.” 


122 


NOTES ON CHEMICAL ANALYSIS 


Cadmium as Sulfate.—In the absence of electrolytic apparatus, 
the H 2 S 0 4 solution after concentration and the expulsion of 
most of the acid may be transferred to a weighed crucible, 
evaporated to dryness and heated sufficiently to drive off all 
excess H 2 S 0 4 by manipulating the crucible in the flame. The 
theoretical factor for CdS 0 4 is used. If Cu is present an error 
may be introduced by the partial decomposition of its sulfate. 
It is better, therefore, to separate Cu by the precipitation of CdS 
from the cyanide solution before the determination. 

Iron.—So much has been written about the Fe determination 
that further discussion would seem to be superfluous. A few 
hints and reminders, however, may not come amiss. 

It is rarely safe to determine small amounts of Fe by weigh¬ 
ing the oxide. Too many impurities are likely to be included 
in the precipitate. Instead it is better to use a small reductor 
made of a 25 cc. burette or a tube of the same size. The form 
shown in Fig. 15 is easily made from tubing of any size. By 
the use of blanks on the reductor as corrections on determina¬ 
tions, and dilute KMn 0 4 , the error of the determination may be 
kept as low as 0.0002 gram. 

It should be remembered that the filtration of an acid solu¬ 
tion produces more or less sugar from the paper, and also that 
traces of HN 0 3 produce comparatively large reducing effects 
on passage through the reductor. Greater accuracy, therefore, 
is obtained by evaporating the H 2 S 0 4 solution to fumes and 
while hot adding a small crystal of KMn 0 4 before passing 
through the reductor. 

As most rocks contain traces of Ti, some account needs to be 
taken of its presence in ore analysis. Traces of Ti have no 
appreciable effect on the KMn 0 4 titration of Fe, as Ti is easily 
oxidized by dropping through the air from the reductor to the 
flask. If much Ti is present, the H 2 S reduction is convenient. 
Fresenius 7 describes the method carefully. As a precaution, 
it is useful to test the solution with KCNS to see if the Fe is 
reduced before boiling out the H 2 S. KCNS ordinarily con¬ 
tains some oxidizing material which will give a reaction for 


7 Fresenius. “Quantitative Chemical Analysis.” Vol. I. 


determinations 


123 



ferric iron even when the Fe tested has been entirely reduced. 
In order to get negative results for trivalent Fe, it is necessary 
to treat some KCNS solution with S 0 2 , and boil out the excess, 
before using it. Commenting on Fresenius, the apparatus 
shown in Fig. 14, using a bicarbonate solution, is convenient for 
boiling out H 2 S and cooling the solution. 

Aluminium.—A 1 is determined by weighing its oxide. In most 
cases it is necessary to weigh other elements with it; Fe 2 0 3 , 
TiO z , and P 2 O s . The treatment of this mixture will be dis¬ 
cussed under Separations. 

A 1 2 O s requires the full heat of the blast lamp for its com¬ 
plete dehydration. Such a temperature will reduce Fe partly 


















124 


NOTES ON CHEMICAL ANALYSIS 


to Fe 3 0 4 . Ordinarily a balance of errors is obtained by a 
moderate blast heat with thorough oxidation. Fortunately 
highly accurate determination of A 1 are rarely necessary. 

Chromium.—Small amounts of Cr are determined by weigh¬ 
ing the oxide, Cr 2 0 3 and larger quantities by reduction from 
hexavalence to trivalence. 

The method of reducing the chromate by ferrous salt and 
then titrating the excess ferrous salt with KMn 0 4 is described 
by Scott. 8 The greatest difficulty in the use of this method 
is in distinguishing the end point of pink through the green of 
the reduced Cr. In the laboratory of Lucius Pitkin, Inc., an 
old carbon filament lamp, which gives a reddish light, is placed 
behind the beaker in a rather dark room. This makes the green 
almost invisible, and shows the pink clearly. 

The determination of the end point correction is another 
difficulty. A fairly good way is to allow the end color to fade 
entirely after a titration and then to add more KMn 0 4 to a 
pink. By testing several which have stood for different lengths 
of time, a fair approximation to the proper correction can be 
obtained. This, however, will hold good only for about the 
same amount of Cr. On account of the back titration, the ordi¬ 
nary algebraic solution from standard chromate is too compli¬ 
cated for practical use. 

Vanadium.—V is reduced from V 2 0 5 to V 2 0 4 by repeated 
evaporation with HC 1 . Other elements such as Cr and Fe do 
not interfere, so that it is possible to assay most ores for V 
without separations. 

Having the V in solution in either HC 1 or H 2 S 0 4 , HNO s be¬ 
ing absent, add KMn 0 4 solution in excess to make sure that no 
other substances which will reduce KMn 0 4 remain. Then add 
H 2 S 0 4 enough to total 20 cc. and HC1 to total 50 cc. Evaporate 
at a low temperature on the hot plate uncovered to incipient 
fumes of S 0 3 , cool, add a little water and 25 cc. of HC 1 and re¬ 
peat. For samples high in V a third evaporation is advisable. 
Finally cool, dilute to 200 cc., heat on the water-bath to dissolve 


8 Scott, “Standard Methods.” 


determinations 


125 


all cakes and crystals of Fe 2 (S 0 4 ) 3 , and titrate hot with KMn 0 4 
to the first appearance of pink throughout the solution. 

Reduction of Vanadium by Sulfur Dioxide.—V may be reduced 
completely to tetravalence by the addition of a small excess of 
SO a to the H 2 S 0 4 solution. The excess is boiled out and the 
solution titrated hot. The operation is best carried out in a 
Florence flask half full. Paper moistened with fuchsine solution 
will bleach in the steam containing S 0 2 . Or the steam may be 
smelled occasionally and the solution boiled for fifteen minutes 
after the S 0 2 can no longer be detected . 

Electrolytic Reduction of Vanadium.—Perfect reduction of V 
to V 2 0 4 is obtained by passing an electric current through the 
H 2 S 0 4 solution. This method is suitable for accurate work on 
high grade material. 

Uranium.—Gooch and Pulman’s method is used, in which the 
sulfate solution is passed through a reductor and titrated with 
KMn 0 4 . 9 

Some of the author’s recommendations for the use of the re¬ 
ductor seem to the writer unnecessary. It is important not to 
allow air to pass through the reductor, but the acid may be 
diluted as low as 2 per cent, and the solution need not be hot, 
thus avoiding all trouble from H in the reductor. If the flask 
be shaken for one minute and the solution titrated in the flask, 
as concordant results as are possible are obtained. On account 
of the high atomic weight of U, KMn 0 4 about 0.05 N should be 
used. 

It is necessary to establish a blank correction by going through 
all the operations of separating the elements which interfere; 
particularly Fe and V, if they are found in the samples to be 
analysed. The corrections for different materials may vary as 
much as from 0.3 cc. to 0.8 cc. A fixed scheme should therefore 
be used with its correction for each type of sample. The com¬ 
mon types are, 1, Alloys; 2, Carnotite ores containing V; 3, 
Pitchblende, containing no V; 4, Uraninite, manufactured 
products and concentrates high in U. 

Zinc.—Low’s method is recommended. 10 The writer pre- 

9 Gooch. “Methods in Chemical Analysis.” 

10 i, ow . “Technical Methods of Ore Analysis.” 

9 


126 


NOTES ON CHEMICAL ANALYSIS 


fers a few variations. Uranium acetate gives a slightly better 
end color than the nitrate. A rubber-tipped rod is convenient 
for stirring, as there is less danger of breaking the beaker, and 
less wear on it. Lifted horizontally out of the beaker it will 
hold enough solution for the test. 

It is convenient to divide the solution into two equal portions 
in beakers of the same size before titrating, and to keep one- 
half hot while titrating the other roughly. Then all but enough 
to account for i cc. of the standard solution is poured from 
the original beaker into the extra one and solution measured 
in to within a few cc of the expected end. Then the end is 
approached i cc. at a time, and when the color is obtained, the 
solution, now spent, is poured into the original beaker without 
washing, and the titration finished o.i cc. at a time. 

The extra beaker can then be used without rinsing for the 
next titration. 

Before titrating, the solution should not be heated long enough 
to expel all the H 2 S. Otherwise the chlorate, which is not all 
destroyed during the separations, will begin to act, causing a 
green color and high results. A blue color is produced by a little 
Fe, but this will disappear before the end, and does not produce 
an error. Indeed, it is a useful aid to the titration. Some use it 
as an indicator. 

In the separations, the writer prefers 250 cc. beakers to flasks. 
They allow more rapid evaporation and are easier to police. 

In filtering, no stirring rod is necessary. The policeman is 
used for the first pouring. The sides and bottom of the beaker 
are then rubbed. By this time the filter is empty. Fill it again, 
rinse and remove the policeman, and proceed to the next beaker. 
A third pouring will empty the beaker, and the drop can be 
touched off on the edge of the filter. 

The leaching solution may contain ammonium persulfate in¬ 
stead of bromine water. Enough is used to give 0.25 gram per 
sample. 

Low uses only one separation. This is enough for most ores. 
Occasionally, an ore turns up in which two separations are neces¬ 
sary, so that it is safer to use two in all cases of doubt. For the 


determinations 


127 


second separation, the original beaker is placed under the funnel, 
the paper opened at the bottom with a metal point and the bulk 
of the precipitate washed through. 10 cc. of HC 1 poured 
around the paper with one washing will clear the paper. The 
HC 1 is used for its superior solvent effect. It is evaporated to 
dryness, replaced by HN 0 3 , and the KC 10 3 treatment etc. re¬ 
peated. If the sample needs no HC 1 treatment it is not likely 
that a second separation is necessary, though for safety one may 
use HN 0 3 to dissolve the precipitate, adding the KC 10 3 when 
the solution has evaporated to 5 cc, with less work. 

Nickel and Cobalt.—The electrolytic method is the most accu¬ 
rate, and in many cases is all that is necessary, the two metals 
being reported together. 11 

If there is a considerable amount of Co, so that the error of 
the differential method is not too large in proportion to it, it is 
best to dissolve the two metals from the cylinder and determine 
Ni as glyoxime. 12 If there is but little Co, it is best to deter¬ 
mine it by nitroso beta naphthol and take Ni by difference. 12 

This method as described is troublesome, as the reagent pre¬ 
cipitates when it is added to the main solution, leaving the suc¬ 
cess of the Co precipitation in doubt. If the solution containing 
the sample be made 15 per cent acid with acetic acid, the reagent 
itself will not precipitate, and the Co precipitate can be clearly 
seen. This makes the method a good qualitative test for Co, 
and the quantitative determination is more convenient and re¬ 
liable. The solution should stand for at least an hour before 
filtering, as the precipitate collects slowly. If it is allowed to 
stand over night, a small brown precipitate of the reagent may 
form in the absence of Co, which is easily distinguished from 
the flesh red of the Co precipitate. 

Calcium.—Ca in small amounts is best determined as oxide by 
ignition of the oxalate at blast temperature. In larger amounts, 
or where the small error of the end point is negligible, the oxa¬ 
late should be titrated. 13 

11 Smith, “Electro-Analysis.” Scott, “Standard Methods.” Dow, “Ore Analysis.” 

12 Scott, “Standard Methods.” Dow, “Ore Analysis.” 

is Fresenius, “Quantitative Analysis.” Scott, “Standard Methods.” Low, “Ore 
Analysis.” 


128 


NOTES ON CHEMICAL, ANAEYSIS 


If the titration method is to be used, it is not necessary to 
police the beaker, but it is necessary to wash both beaker and 
rod several times with hot water to make sure that the adhering 
crystals are washed free from the precipitant. 

It is best to use an empirical factor based on the particular 
method of precipitation and washing. In the laboratory of 
Ledoux & Co., the iron value of the permanganate is multiplied 
by 0.5048 instead of the theoretical 0.5020. 


CHAPTER VIII 

SEPARATIONS 

Tin from Other Elements.—Having the Sn in the form of SnS 2 
mixed with other sulfides, filter with pulp and wash with i per 
cent H 2 S 0 4 , by decantation (page 73) if the size of the pre¬ 
cipitate or the quantity of the lower group elements seems to 
make it necessary. Treat the precipitate with stock alkali solu¬ 
tion (page 64) and filter. Reserve the filtrate. If the residue 
is very small it may be assumed that the separation is complete. 
If it is large, some Sn will certainly remain with it. Put paper 
and residue back into the beaker, add 10 cc. of H 2 S 0 4 and de¬ 
stroy the paper with HNO s (page 74). Cool, dilute, boil, and if 
PbS 0 4 appears, the solution being otherwise clear, cool and fil¬ 
ter. If a white milky residue appears, with or without PbS 0 4 , 
add just enough HC 1 to dissolve it by boiling. 

Having a clear solution, dilute to about 150 cc. and pass H 2 S 
into the hot solution, without regard to whether Pb is precipi¬ 
tated or not. Filter and treat the precipitate with stock alkali 
as before, using as little as possible to make the mixture decidedly 
alkaline. Combine the two alkaline solutions, which should 
contain all the Sn and Sb, but perhaps not all the As. By taking 
care of the acidity and temperature of the solutions, the alkali 
insoluble elements may also be completely separated, with the 
exception of Cu, a little of which will afterward be found with 
the Sb. 

In case the residue insoluble in alkali cannot be washed with 
hot water without running through, dilute NH 4 S X may be used. 
In some cases, as where there is much Bi, it may be necessary 
to use NH 4 SH instead of stock alkali. The objections to using 
this reagent in all cases is that Cu is somewhat more soluble in 
it and the quantity of S and of salts admitted is larger. 

Having all the Sn in alkaline solution, add Na 2 0 2 a little at a 
time with stirring until the solution becomes colorless. Boil 
for fifteen minutes and add solid oxalic acid to the hot solution 
until litmus paper turns red, and three to five grams in excess. 
As the method is used only for small amounts of Sn, this amount 


130 


NOTES ON CHEMICAL ANALYSIS 


of oxalic acid is generally enough. If a slight precipitate forms 
from incomplete decomposition of the sulfides, boil until all SnS 
is dissolved. Dilute to ioo or 200 cc. with hot water and pass 
H 2 S to precipitate all Sb and As. In the absence of HC 1 Sn has 
no tendency to reduce and form SnS. Filter and wash with 1 
per cent H 2 S 0 4 containing no H 2 S. The precipitate contains all 
the Sb, which may be determined by titration. 

The filtrate contains the Sn. The precipitate may, if it is large 
or if there is much Sn in the sample, contain a little Sn. This 
may be separated by washing the precipitate back and dissolving 
it with Na 2 0 2 and repeating the oxalic acid separation, using in 
this as small volumes and as little reagent as possible. 

Having the Sn in oxalic acid solution, free from all other ele¬ 
ments of its group, there are two methods of getting it out. One 
method 14 is to add NH 2 OH in excess, pass H 2 S if necessary to 
get the Sn into solution, filter away any FeS that may appear, 
and make the solution acid with acetic acid. Sn will separate 
at first white, afterward assuming its natural color. Walter 
Spuhr and the writer have both found that this method gives 
low results, but when the tests were made there may have been 
losses by volatilization of SnCl 4 . Further experiments are nec¬ 
essary. The other method 15 the writer can vouch for. That is 
to add enough H 2 S 0 4 to the oxalic acid filtrate to keep all bases 
in liquid form and boil down to fumes, destroying all oxalic 
acid. Take up with water, add KMn 0 4 to a slight pink, then if 
necessary add a little HC 1 to dissolve Sn, filter from Si 0 2 , and 
precipitate SnS 2 . The precipitate is filtered, washed with 1 per 
cent H 2 S 0 4 and weighed as Sn 0 2 . This is preferable when the 
determination is to be both qualitative and quantitative. If Sn 
is known to be present in quantity, the solution after fuming may 
be transferred to a flask, reduced with nickel and titrated with 
iodine. 

Separation of As from Other Elements.—By distillation of 
AsC 1 3 arsenic can be separated in convenient form for deter¬ 
mination from all inorganic materials. 


14 Crooks. “Select Methods in Chemical Analysis.” 
16 Fresenius. “Quantitative Anatysis.” 


SEPARATIONS 


131 

Most of the apparatus described is unnecessarily complicated. 
When As is trivalent it distils readily from an ordinary distilling 
flask containing HC 1 as strong as 50 per cent of the reagent, only 
requiring to be washed out by repeated additions of acid. 

Pentavalent As requires first to be dissolved, second to be 
treated with a reducing agent in presence of hot concentrated HC 1 . 
This also can be done in any kind of distilling flask. 

Getting Arsenic into Soluble Form.—Alloys cannot be treated 
with HC 1 on account of the formation of arsine. Weigh from 
0.5 to ten grams of the alloy sample into a round-bottomed dis¬ 
tilling flask of 250 cc. capacity or slightly more. Add just enough 
water and HNO s to dissolve the sample or to oxidize it com¬ 
pletely. If much Cu is present, H 2 S 0 4 may be added at the 
start. With Sn or Pb predominant, it is better to start with 
HNO3 an d water. When the alloy is completely decomposed, 
add H 2 S 0 2 enough to keep it liquid during fuming. For small 
samples 5 cc. is enough. For two to five grams 10 cc. will do. 
For ten grams 20 cc. must be used. 

Set the flask in an evaporating can (Fig. 12) on a hot plate 
and drive off most of the water and HNO a . Add a square inch 
of paper, hold the flask in wooden tongs (Fig. 8) over a flame 
and blow out the remaining HN 0 3 . Heating the acid to boiling 
and blowing a jet of air into the flask for a few seconds for three 
times is enough. There should be enough paper added to leave 
a black residue, which makes it certain that all the HN 0 3 is out 
of the acid at the bottom of the flask. The blowing is depended 
on to clear the sides and neck. 

The use of paper or other organic matter has the other ad¬ 
vantages that it helps to reduce the As. The writer absorbed 
the idea from an unkown source. 

Ores, if they contain only acid soluble As, may be treated in 
the same way as alloy, or by Low’s method. 16 If there is a chance 
that the As is not entirely soluble in acid, as in oxidized Sn or 
Sb compounds or minerals, the sample should be fused with 
Nao 0 2 . This is best done in a porcelain crucible, to avoid any 
suspicion of reduction by flakes of metal afterward. Use as little 

16 Tow. “Technical Method of Ore Analysis.” 


132 


NOTES ON CHEMICAL ANALYSIS 


of the flux as possible, leach it out with the least amount of 
water, wash it into the distilling flask, concentrate some by boiling 
if necessary, add HC 1 and boil again, finally obtaining about 50 
cc. of 50 per cent HC 1 . Much Si 0 2 will separate, but this does 
not interfere with the distillation. 

Having the As in soluble form in the flask free from HNO s , 
add a large excess of anhydrous FeS 0 4 if H 2 S 0 4 has been used. 
If the substance is oxidized and soluble in HC 1 , such as lead ar¬ 
senate, Cu 2 Cl 2 should be used. Five grams of the FeS 0 4 or two 
grams of Cu 2 Cl 2 are generally enough. Wash down the neck of 
the flask with a little water. This will help to prevent bumping. 
If the sample contains Se or Te, the addition of HC 1 to concen¬ 
trated H 2 S 0 4 will volatilize them, contaminating the distillate. 
The water precipitates them, after which they are not volatile. 

Connect the flask with the condenser, which dips into about 
100 cc. of cold water in a beaker, pour in 75 cc. of HC 1 through 
the funnel, and simmer gently for about an hour, afterward rais¬ 
ing the heat to distil most of the acid more rapidly. Make two 
additions of 25 cc. each of HC 1 , boiling down to about 25 cc. 
after each. The secret of success is to have the sample dissolved 
with the reducing agent in hot concentrated HC 1 . Fig. 16 shows 
the apparatus used in the laboratory of Ledoux & Co. 

If the As is trivalent in the sample, or if it is desired to dis¬ 
tinguish between trivalent and pentavalent As, the same amount 
of HC 1 is added directly to the sample in the flask, without re¬ 
ducing agents, and the distillation conducted rapidly. For samples 
high in As a Bunsen valve, such as is shown in Fig. 5, with the 
tip drawn to a tapering point and fitted with a ferule of rubber 
tubing, is set in the neck of the funnel, so that air may enter 
during the pulsations of the distillation, but vapors from inside 
cannot escape. Such a valve will last a long time if it is well 
washed after each use. 

The distilling apparatus is fitted with “sulfree” rubber stop¬ 
pers, which keep their shape better than the ordinary kind, last 
longer, and do not distil H 2 S when first heated with HC 1 . 

On account of the H 2 S 0 4 and salts present, there is always a 
possibility of distilling a little Sb with the As. For this reason, 


SEPARATIONS 


133 



Fig. 16 . 


4 



































































134 


NOTES ON CHEMICAL ANALYSIS 


when reducing agents have been used and the percentage of As 
is low enough, it is better to weigh it than to titrate it. By making 
sure that there is 60 per cent or more of HC 1 in the distillate, As 
can be separated from Sb by H 2 S. 

Antimony in Ores.—While most of the Sb in ores is in the 
form of stibnite, weathering often produces more or less oxide, 
which is not soluble in acid. As there is danger of loss when the 
residue insoluble in acid is ignited preparatory to fusing, it is 
safer and simpler to fuse all samples at the start. It is possible 
to save the insoluble by filtering it on the apparatus shown in 
Fig. 6, drying the residue instead of igniting it before fusion, but 
for ordinary ores this is too much work. 

Use an iron crucible of 75 cc. capacity and weigh into it enough 
of the ore to contain something less than 0.3 gram of Sb. Add 
about eight grams of Na 2 0 2 , mix well with a smooth spatula and 
fuse thoroughly, (page 84) Leach in a 400 cc. crucible, add 60 cc. 
of HC 1 quickly to prevent precipitation of Si 0 2 in a neutral solu¬ 
tion, and heat on the water-bath until all iron scales are dissolved. 
There should be a clear solution. If Si 0 2 separates it will be 
necessary to make a fresh start, using more water to leach the 
melt and more acid added quickly. This never occurs in a rich 
ore, and need not occur in any sample weighing less than two 
grams. 

When the solution is clear, dilute it to 300 cc. with hot water 
and pass a brisk stream of H 2 S. Sb particularly needs the extra 
gas pressure and agitation produced by a rapid stream of the gas, 
though it may be passed to saturation slowly, and increased only 
at the end. 

Filter and wash with 1 per cent HOI. It is particularly neces¬ 
sary in case of large Sb precipitates to wash by decantation 
(page 73), as there is much Fe in the solution. If the color of 
the solution and the precipitate shows that there is little or no 
Cu, wash the precipitate back and clear the paper by pouring 
a little stock alkali (page 64) through it, and give it a good wash¬ 
ing with hot water. If more than a few milligrams of Cu are 
present, it will be necessary to treat the entire precipitate. To 
make sure that there is no Sb lost, unless the amount is very small 


SEPARATIONS 


35 


treat the residue with H 2 S 0 4 and HN 0 3 to destroy the paper, 
take up with water and about io per cent of HC 1 to prevent the 
precipitation of Pb, and repeat the separation. Evaporate the 
combined alkaline solutions if necessary to 75 cc., and to the 
warm solution add an excess of KC 10 3 and 50 cc. of HC 1 . Stir 
until all sulfides are decomposed, as shown by the pale color of 
the residual S, boil down to 75 cc., reduce as directed on page 112 
and titrate. 

Separation of Small Amounts of Lead and Iron from Large 
Amounts of Tin.—The sample should be in HC 1 solution with 
the Sn all stannic. Saturate some NH 4 OH with H 2 S, 10 cc. per 
gram of the sample, or more if the sample is small. Add NH 4 OH 
in excess to the solution containing the sample and stir in the 
NH 4 SH quickly. After stirring and settling the solution should 
show clear yellow. If it does not, add more NH 4 SH, which may 
not have been thoroughly saturated. After settling, filter and 
wash with NH 4 SH, keeping the upper edge of the paper wet with 
washing solution during the filtration to prevent the hardening 
of SnS 2 , return paper and precipitate to the beaker, boil with 
dilute HNO s , then add H 2 S 0 4 and destroy the paper, and pre¬ 
cipitate the Pb as usual. On dilution, if the PbS 0 4 appears clean, 
separate it. If not, add HC 1 enough to clear the solution, dilute 
until the HC 1 is not more than 2 per cent of the volume, pass 
H 2 S, filter, treat the precipitate with stock alkali, and separate 
the Pb as usual from the residue. 

If the PbS 0 4 is clean after the first separation, the Fe will 
be found in the H 2 S 0 4 filtrate, but H 2 S must be passed to sep¬ 
arate a small amount of Sn before Fe can be separated. The 
Fe obtained in the filtrate should be titrated. Cu, if present in 
small amounts, can be separated from the H 2 S precipitate. 

Separation of Small Amounts of Lead and Iron from Large 
Amounts of Antimony.—If the NH 4 SH separation described above 
does not work well, take a fresh sample, add tartaric acid to the 
HC 1 solution and NH 4 OH in excess, which will form no pre¬ 
cipitate if enough tartaric acid is added. At least 2 molecules of 
the acid to an H equivalent of the metal are necessary. Pass 
H 2 S, or, for traces, add a measured amount of H 2 S water, which 


136 


NOTES ON CHEMICAL ANALYSIS 


will precipitate Fe, Pb, Bi, and Cu. Filter, dissolve the precipi¬ 
tate and destroy the paper, and proceed as above, separating the 
elements by the direct scheme. As much Cu can be obtained by 
this method as by any other, as it is soluble only in polysulfide, 
which is not formed unless H 2 S is in excess. 

Separation of Copper from Much Tin and Antimony.—Concen¬ 
trate the HC 1 solution by evaporation to a syrup, add tartaric 
acid in excess over the Sn and Sb, then KOH in excess, which 
will form no precipitate. Add an excess, or, preferably, KSH 
formed by saturating KOH with H 2 S. Warm until the precipi¬ 
tate settles, filter and wash with hot water or with hot stock al¬ 
kali. Disolve the precipitate and fume off the paper with H 2 S 0 4 , 
separate the PbS 0 4 if it is clean, or dissolve it in HC 1 and make 
the regular H 2 S separation. 

Copper in Ores.—The possibility of acid insoluble Cu in ores 
is generally disregarded. 

Weigh one or two grams of the ore into a beaker, add 20 cc. of 
water and 10 cc. of HNO s , warm and concentrate until the sul¬ 
fides are decomposed. Add 10 cc. of H 2 S 0 4 , put a hook under 
the cover and slowly expel the HNO : „ finally heating to copious 
fumes of S 0 3 . Cool, dilute, add just enough dilute NaCl solu¬ 
tion to precipitate the Ag, dilute, boil and filter. If the ore con¬ 
tains no impurities which will interfere with the clean separa¬ 
tion of Cu, add from 5 to 7 cc. of HNO s and electrolyse. 

Sulfocyanate Separation.—This method is used to separate Cu 
from elements which interfere with the electrolysis, and is suc¬ 
cessful for almost every kind of material. It is possible to begin 
with a solution containing a few cc. of HN 0 3 , though a sulfuric 
or hydrochloric solution is preferable. Ordinarily the solution 
used is that which would otherwise have HNO s added to it for 
the electrolysis; either an aliquot from bar copper dissolved in 
H 2 S 0 4 with a minimum of HN 0 3 , the Ag having been separated 
during the solution; or the H 2 S 0 4 filtrate from an ore, the HN 0 3 
having been expelled and the AgCl precipitated before filtering. 
The solution should be hot or warm. 

Add NH 4 OH to the solution until a precipitate forms, care¬ 
fully dissolve it with as little HC 1 as possible, add about 10 cc. 


separations 


137 


of 20 per cent NaHS 0 3 , stir, and if there is a large amount of 
Fe which seems not to be reduced, add more. Then add 5 cc. 
of 5 per cent KCNS solution and stir well. If it is in excess 
over the Cu, it will give a red color with the still unreduced Fe. 
If no red, but a large white precipitate appears, add 5 cc. more 
of the precipitant, as the Cu is still in excess. The red should 
disappear on standing warm for a few minutes, but its appear¬ 
ance is the best indication that the KCNS is in excess. After 
the solution has become almost or quite colorless through the 
reduction of Fe, filter with pulp or on double papers, the outer 
paper being a size smaller than the inner, wash out the beaker 
and the top of the filter once with hot water. 

Much washing with water will cause the precipitate to run 
through. The ignition is depended on to complete the separation. 
If more washing is desired, it can be done with a solution of 
(NH 4 ) 2 S 0 4 . Do not police the beaker but after the filtration 
wipe it out with a piece of filter paper. Any little rolls of paper 
left in the beaker can then be washed into the filter. Transfer 
the precipitate and papers to a silica crucible and roast carefully 
to expel all chlorides, and then to char off the paper without 
flame, with plenty of fresh air. The roasting is the critical part 
of the operation. It can be done singly over a Bunsen burner, 
but where quantities of crucibles are to be cared for this is not 
safe. A specially made muffle, heated by gas, or preferably by 
electricity, which will give the right conditions when the heat 
is turned on full, is the most reliable. 

After the roasting the small residue of charred paper is burnt 
off over a Bunsen burner, the full heat being used. There should 
not be the least sign of green in the flame, as this shows that Cu 
is lost. 

Add 5 cc. of HNO s to the ignited residue, or more if the 
amount of Cu is large, cover the crucible with a small cover 
glass, warm to dissolve, boil for a minute, transfer to a beaker, 
add H 2 S 0 4 and electrolyse. There should be little if any red 
fumes during solution with HN 0 3 . Their appearance is evidence 
of improper roasting. The method requires attention to every 
detail for success, but the results are accurate, never high. It 


i 3 § 


NOTES ON CHEMICAL ANALYSIS 


can be easily taught to an assistant by one who has learned the 
use of his apparatus. 

Lead in Ores and Waste Materials.—Unless the presence of in¬ 
terfering impurities is known, direct H 2 S 0 4 treatment is first 
tried. Weigh one gram of the material into a 400 cc. beaker, add 
20 cc. of water and 10 cc. of HN 0 3 , warm and concentrate until 
sulfides are decomposed. In the case of red lead or other ma¬ 
terial containing peroxides, a reducing agent such as alcohol is 
necessary. Add 10 cc. of H 2 S 0 4 and boil down to fumes of SO s . 
Take up with 80 cc. of water, boil, and if the residue appears to 
be free from gummy or milky adhesions and shows the charac¬ 
teristic dead white finely granular appearance of PbS 0 4 , proceed 
with the conversion of PbCr 0 4 . (Page 116). 

If the residue insoluble in ammonium acetate is transparent 
quartz or some other known material which contains no Pb, it 
may be disregarded and the separation considered complete. 

INTERFERING ELEMENTS IN THE LEAD ASSAY 

Bismuth.—In the above separation Bi, if present, may cause 
an error without showing any insoluble precipitate. Part of it 
will dissolve completely in dilute H 2 S 0 4 and the rest will go with 
the Pb, giving a high result. In case of doubt a qualitative test 
for Bi should be made before precipitating the Pb as PbCr 0 4 . 
Add NH 4 OH to the acetate solution. Pb will remain in solution 
and Bi will precipitate. Filter at once, as Pb is precipitated 
slowly. Wash the filter with hot water, return it to the beaker, 
add 5 or 10 cc. of H 2 S 0 4 , destroy the paper and repeat the separa¬ 
tion. In most cases the separation will be complete on the second 
precipitation. There will be a balance of errors, some Pb being 
lost in the extra fuming to counterbalance the trace of Bi that 
may be left. Where the highest accuracy is desired, a check 
assay on a known amount of Pb and Bi will indicate the neces¬ 
sary correction. 

Antimony in the Lead Assay.—When Pb and Sb are evaporated 
to fumes together, as much as 0.005 gram of Sb will remain in 
solution and cause no error. A compound insoluble in acetate 
may be decomposed by fuming off the paper and repeating the 


SEPARATIONS 


139 


separation. When the amount of Sb is known to be near the 
limit of separability, as in the case of impure lead bullion, fil¬ 
tering the PbS 0 4 , returning it to the beaker and fuming off the 
paper may be enough. 

A residue which is insoluble in ammonium acetate, but which 
is filterable, should be ignited carefully, fused in sulfur and soda, 
leached, filtered, washed with NH 4 SH, and paper and precipitate 
boiled with dilute HNO e , and then fumed with H 2 S 0 4 , the ace¬ 
tate solution being combined with the main portion. When the 
acetate is obtained in two portions it is best to divide the 5 cc. 
of acetic acid used for washing between them, so that there may 
not be too much in the precipitation of the chromate. 

A milky residue may remain which runs through the filter, 
interferes with the acetate separation, and leaves the assay in 
doubt. When this is encountered in the course of a long analy¬ 
sis, it is best to stop the filtration, return paper and precipitate 
to the beaker, fume off the paper, take up with HC 1 and resort 
to the H 2 S separation. When it occurs in a lead assay, the best 
thing to do is to start again, by fusing the entire sample with 
sulfur and soda. 

Tin in the Lead Assay.—If a small white precipitate forms in 
the dilute H 2 S 0 4 which is known to be Sn and not Sb, as in 
the analysis of pig tin, it may be ignored. It does not hold lead 
or interfere with the chromate precipitation. 

Calcium in the Lead Assay.—A small amount of Ca will remain 
in solution in dilute H 2 S 0 4 and will not interfere. CaS 0 4 crys¬ 
tals are easily recognized, as they are large and transparent. If 
they are seen, proceed with the solution in acetate, but instead 
of precipitating with chromate, pass H 2 S, which precipitates only 
Pb, filter and convert the sulfide to sulfate. The Ca may be 
completely recovered in the two filtrates. 

Barium in the Lead Assay.—Many pigments contain lead and 
barium compounds loosely mixed. From these Pb can be com¬ 
pletely separated by boiling with HC 1 , the Ba remaining insoluble 
and Pb dissolving in the hot moderately dilute acid. From the 
HC 1 solution Pb is precipitated with H 2 S and recovered as chrom¬ 
ate. 


140 


NOTES ON CHEMICAL, ANALYSIS 


If Ba and Pb are evaporated to fumes together a mixed resi¬ 
due insoluble in acetate is formed. The sulfur and soda fusion 
will not completely decompose it. After the acetate treatment, 
ignite the residue carefully in a nickel crucible. Fuse with mixed 
Na 2 C 0 3 and K 2 C 0 3 . Leach with water, police and remove the 
crucible. Add a little NaSH to precipitate any Pb that may be 
in solution, filter and wash with hot water. Wash the precipitate 
back, add acetic acid to decompose the carbonates, treating the 
paper also, pass H 2 S just long enough to precipitate the Pb, and 
filter. Most of the Ba will remain in the filtrate. Recover the 
Pb from the precipitate and add it to the main portion. This 
separation was worked out in the Navy Laboratory at Washing¬ 
ton. 

Separation of Lead as Chloride.—The table of solubilities for 
Pb in different HC 1 solutions given on page 51 shows that if 
the solution is boiled down to constant proportion of HC 1 and 
two volumes of water added, the solution on cooling will contain 
the minimum quantity of Pb for the amount of HC 1 present. 
The PbCl 2 can be filtered and washed with 5 per cent HC 1 and 
diluted indefinitely without any further separation of PbCl 2 . 
This gives a convenient method for separating the bulk of the 
Pb from alloys high in Pb. 

Lead in Clean Alloys.—Weigh one gram into a 250 cc. beaker. 
Add 40 cc. of water, 30 cc. of HC 1 and 3 cc. of HNO s . Heat 
the mixture almost to boiling until the alloy is dissolved, put a 
hook under the cover and boil down slowly to a volume of about 
30 cc. Add double the volume of water, stir and let stand until 
cold. Filter on a seven centimenter paper, wash with 5 per cent 
HC 1 , dissolve the chloride in ammonium acetate and reserve it. 

If the sample contains little or no Cu, saturate 25 cc. of 1 :i 
NH 4 OH with H 2 S, add NH 4 OH in excess to the filtrate from 
the PbCl 2 and stir in the NH^SH. After the precipitate has 
settled filter and wash with NH 4 SH. Return the precipitate 
and paper to the beaker, boil with HN 0 3 114 until the sulfides 
are decomposed, add 5 or 10 cc. of H 2 S 0 4 , fume off the paper, 
separate the Pb as sulfate, add the acetate solution to the main 
portion and precipitate as chromate. 


SEPARATIONS 


141 

The filtrate from the PbS 0 4 will contain all the other elements 
except the tin group. Traces of the tin group will be found in 
this filtrate, and must be separated by another H 2 S separation 
before electrolysing the Cu. 

If the sample contains Cu, ammonium sulfide does not work 
well. Add tartaric acid to the HC 1 filtrate, make it alkaline 
with NaOH and add a slight excess of NaSH. Warm the mix¬ 
ture until the precipitate has settled, filter and wash with hot 
water, dissolve the residue in H 2 S 0 4 by fuming off the paper, 
separate PbS 0 4 and the other elements as usual. 

Lead in Impure Metallic Mixtures.—Drosses containing particles 
of metallic lead, or buttons obtained from the fire assay of drosses, 
in which different alloys are segregated, should be hammered 
into fine particles or thin sheets. As much as twenty grams can 
be used. For that amount use an 800 cc. beaker. There are two 
methods of solution. If nitrates are to be avoided, add about 
300 cc. of HC 1 and heat to about 8o°, adding more acid if neces¬ 
sary to keep PbCl 2 in solution, until the evolution of H ceases. 
Then add KC 10 3 a little at a time until Cl is in excess and all 
metal is dissolved. Boil the solution until PbCl 2 begins to sep¬ 
arate. Add two volumes of water, stir, and let stand until cold. 

The other method is to make up a mixture of thirty parts HC), 
forty parts water, and three parts HNO s . Begin with 400 cc. of 
the mixture and keep some reserve solution hot. Boil and keep up 
the volume with the reserve until the metal is all dissolved. If 
there are pieces of dense iron alloy which do not dissolve, they 
should be removed by decantation, ground fine and treated sep¬ 
arately. Put a hook under the cover and boil down slowly until 
the PbCl 2 begins to separate. Add two volumes of water, stir 
and allow to cool. 

After cooling, filter into a liter flask, wash with 5 per cent 
HC 1 , dilute to the mark and take an aliquot for analysis. Dis¬ 
solve the PbCL, in ammonium acetate, filter it into another liter 
flask and take a similar aliquot. This may be reserved to chro¬ 
mate when the Pb has been recovered from the main portion. The 
residue insoluble in acetate may be fused or otherwise treated to 
recover the values. 


10 


142 


NOTES ON CHEMICAL ANALYSIS 


BISMUTH SEPARATIONS 

Little Bismuth from Much Lead.—Dissolve the alloy in HN 0 3 , 
precipitate and remove Ag, leaving some excess of HC 1 to com¬ 
bine with Bi, and to the hot solution add NH 4 OH until litmus 
paper shows exact neutrality. Allow the precipitate, which con¬ 
sists of basic bismuth nitrate or chloride and a little basic lead 
hydrate, to settle, filter and wash with hot water, disregarding 
the precipitate which forms in the filtrate. Dissolve the precipi¬ 
tate in HNO s , evaporate to dryness on the water-bath and pre¬ 
cipitate Bi as BiOCl. 

Little Bismuth from Much Antimony and Other Elements.— 

Place 5 grams of the ore or other material, or, if it is a lead 
alloy, as much as is desired, in a scorifier, add enough test lead 
to make eighty grams in all, and scorify to a fifteen-gram button 
Dissolve this and recover the Bi as above. This method is suitable 
only for low percentages of Bi, as there is some loss when large 
amounts of Bi are scorified. Tests should be made to determine 
the limits of the method for the conditions of the laboratory. 

Separation of Much Bismuth from Customary Impurities.—Dis¬ 
solve the sample in HNO a . If there is an insoluble residue, filter 
it on a Gooch filter with a bell jar into a beaker. Dry the resi¬ 
due, transfer it to a crucible and fuse it with Na 2 0 2 . Acidulate 
the solution with HC 1 , dissolve or filter off the insoluble, and 
precipitate the two solutions separately with H 2 S. Filter on the 
same filter, treat the precipitate with NH 4 SH and wash with the 
same. Wash back the residue, add io cc. of HNO s and enough 
water to make the solution 20 per cent, and boil until the sulfides 
are decomposed. Filter, wash with hot 5 per cent HNO a and 
boil out the H 2 S from the filtrate. Filter again if necessary, on 
the same filter. Destroy the paper and dissolve the residue in 
H a S 0 4 , which will separate the remaining Bi from S. Dilute, 
boil and filter. Precipitate the two solutions separately with 
(NH 4 ) 2 C 0 3 ,. This is done by adding NH 4 OH almost to neu¬ 
trality, and then adding an excess of powdered carbonate. Boil, 
let stand to cool, filter, dissolve the precipitate in HN 0 3 , evapor¬ 
ate the solution to dryness and precipitate BiOCl. 


separations 


143 


Separation of Bismuth from Tellurium.—Occasionally a BiOCl 
precipitate will be colored yellow by Te. In this case, take a 
fresh sample, make the ordinary H 2 S precipitation to get rid of 
Fe, treat with NH 4 SH if there appears to be much of the Sn 
group, wash back the BiS, boil with dilute HNO a to dissolve it, 
filter and reserve the residue. Boil out H 2 S from the filtrate, 
add tartaric acid and add NH 4 OH in excess, which should form 
no precipitate. Pass Hj 2 S, which will precipitate Bi free from 
Te. The precipitate may be filtered on the filter containing the 
previous insoluble residue, washed with NH 4 SH, and Bi re¬ 
covered as before. 

Separation of Cadmium from Much Zinc.—Dissolve the sample 
in 20 per cent H 2 S 0 4 , adding a few drops of HNO a from time 
to time if necessary to hasten the solution, but taking care not 
to leave more than 1 cc. excess at the end. This applies, of course, 
only to metal, which will decompose HNO a . If the sample is 
spelter, take from ten to tw r enty-five grams and use 0.85 cc. of acid 
per gram, with addition of 10 to 15 cc. for final excess. When all 
zinc is dissolved, disregarding the small insoluble residue which 
may be mostly Pb, add ten to fifteen grams of (NH 4 ) 2 S 0 4 , dilute 
to an acidity of less than 5 per cent and pass H 2 S. In the absence 
of ammonium salts a little Cd may escape precipitation. Let 
the solution stand to settle, pass H 2 S again and filter. Wash a 
few times with water. Save the filtrate for Fe, if that is to be 
determined. 

Return the paper to the beaker, add 10 cc. of H 2 S 0 4 , destroy 
the paper with HNO s and separate the PbS 0 4 . Dilute the fil¬ 
trate to 4 per cent acidity, add five grams of (NH 4 ) 2 S 0 4 , repeat 
the precipitation, and filter. Add the filtrate to the previous one 
for total Fe. 

If there is a chance of the Sn group being present, treat the 
precipitate with fresh NH 4 SH to avoid loss of Cu, fume off the 
paper again and repeat the H^S separation, using 5 cc. of H 2 S 0 4 . 
Test the filtrate, which should be almost or entirely free from 
Zn. If much Zn shows, some may still be in the precipitate. If 
necessary, repeat the separation. The Cd -f Cu may be deter¬ 
mined by electrolysis as directed on page 121. To determine 


144 


NOTES ON CHEMICAL ANALYSIS 


Cd as CdS 0 4 , add NH 4 OH in excess to the H 2 S 0 4 solution, 
then NaCN solution until the blue of Cu is destroyed, and a 
little more, and precipitate CdS. Dissolve the sulfide in H 2 S 0 4 
by destroying the paper and make the determination as directed 
on page 122. 

Separation of Small Amounts of Copper and Antimony from 
Much Tin.—Dissolve ten grams of the alloy in a mixture of 25 cc. 
of water, 50 cc. of HC 1 , and 10 cc. of HNO s , in an 800 cc. beaker. 
The action will become violent suddenly at the end of the solu¬ 
tion. Boil to make sure of complete oxidation, remove the 
cover and evaporate on the water-bath to small bulk. Dilute to 
200 cc., add concentrated KOH solution in excess, then twenty- 
two grams of oxalic acid and ten grams of ammonium oxalate, 
dilute at once to 600 cc., stir well and heat until all is in solution. 
Pass H 2 S in a vigorous stream to saturation, or pass it slowly for 
fifteen minutes, heat the solution again, and give a rapid stream 
for one minute. Filter, wash slightly with water, treat the residue 
with KOH and filter into a 400 cc. beaker. If the bases did not 
dissolve entirely in oxalic acid on account of the low solubility of 
the oxalates of copper and lead, it may be necessary to fume off 
the paper, take up with HC 1 , add ammonium oxalate, which will 
free some oxalic acid, and repeat the separation. If there is 
much Sb, in any event it will be necessary to get some of it out 
of the filtrate from the PbS 0 4 . There will then be two alkaline 
solutions containing Sb, which may be combined, evaporated to 
75 cc., and determine Sb as directed on page 112. 

The Cu will be found in the final residue after separating the 
last trace of Sb by stock alkali. Some Pb will be in the oxalic 
acid filtrate with Sn, so that it is better to make the lead deter¬ 
mination on a separate portion by NH 4 SH. 

As a small amount of Cu is dissolved by the stock alkali, the 
result will be slightly low. The Cu can be recovered by oxidiz¬ 
ing the alkaline sulfide solution with Na 2 0 2 (page 129). The Cu 
is precipitated as oxide after the sulfides are decomposed. There 
is a possibility of some sodium antimonate being precipitated 
also, but this will not occur unless much Sb is present. It would 


separations 


145 


be an advantage to have for this separation, to make sure 

of keeping Sb in solution. 

Analysis of the Metastannic Acid Precipitate.—This is obtained 
in the analysis of bronze and solder. There are several schemes 
described for precipitating it, but none of them are perfect. In 
any case there will be a trace of Sn in solution, and the precipi¬ 
tate is never pure. If concentrated HN 0 3 or fuming HNO s is 
used on a sample containing S there will be some PbS 0 4 formed. 
It is better, therefore, to use slightly dilute acid. The precipitate 
will contain part of the As, all of the Sb if it is not more than a 
quarter as much as the Sn, some of the Cu, about 0.15 per cent 
in a normal bronze, a large part of the Fe, all of the P, some 
of the Mn, and possibly some Pb. 

For ordinary bronze, weigh three grams into a 250 cc. beaker. 
For solder use 0.5 gram. Add 25 cc. of water and 15 cc. of 
HN 0 3 . Warm until action ceases, boil until red fumes are 
gone, dilute to 100 cc., and allow the precipitate to settle. If it 
stands over night filtration is easier. 

Set a rapid nine-centimeter filter with pulp, filter and transfer 
the precipitate to the filter with cold water. Wash once with hot 
10 per cent HN 0 3 and then several times with hot water. 

Put the precipitate into a weighed porcelain crucible, roast off 
the paper carefully and burn off all carbon. Put the crucible in 
a muffle and heat uncovered for five minutes at a temperature high 
enough to soften porcelain slightly . Then cover and heat for 
fifteen minutes if the temperature is more uniform when the 
crucible is covered; otherwise one heating for fifteen to twenty 
minutes will do. Heating to a high temperature covered without 
preliminary oxidation causes loss. The muffle may be made for 
use with a blast lamp as follows: 

Take two Denver thirty-gram crucibles, knock out the bottoms 
so as to leave holes about one inch in diameter, support one of 
them in a ring over the blast lamp and fit a triangle into the mid¬ 
dle of it. This can be done by fitting a ring of heavy iron wire 
into the crucible and laying a legless triangle on it, or the legs of 
a triangle may be bent down to fit the sides of the crucible. Plat¬ 
inum is best. Nichrome will last a long time. Make a cone of 


146 


NOTES ON CHEMICAL ANALYSIS 


molded asbestos, with a base no larger than the top of the cru¬ 
cible to be heated, set it in the triangle, dry it and burn out the 
carbon. Invert the other Denver crucible on top of the first for 
a chimney, set the blast lamp vertically under and adjust the 
flame to give the proper heat. The full heat of a good blast 
lamp is too much. The flame should be oxidizing, and long 
enough to surround the asbestos cone. Porcelain sticks less to 
asbestos when hot than it does to another piece of porcelain. 

After the muffle is hot, put in the crucible uncovered, heat for 
five minutes, cover and heat for fifteen minutes. When the igni¬ 
tion is properly made, the precipitate is of a uniform color and 
does not stick to the bottom of the crucible. Cool in a dessicator 
and weigh. Constant weight should be obtained at the first heat¬ 
ing, but in starting to use a muffle one should make sure by re¬ 
peated heating of a sample. 

After weighing add from two to five grams of sulfur and soda 
mixture (page 85) and fuse. It is not necessary to mix the 
sample, and the crucible can be heated at once to fusion tempera¬ 
ture for fifteen minutes. 

Leach, filter on an ashless nine-centimeter paper, wash thor¬ 
oughly with NH 4 SH, reserve the filtrate and ignite the residue. 
Weigh the residue, treat it in the crucible with a little HC 1 until 
Cu and Fe are dissolved, dilute, filter, ignite the residue and 
weigh. The difference between these residues measures the 
oxides of Fe, Cu, Pb, etc. They may be determined separately, 
or the HC 1 filtrate can be evaporated with a little H 2 S 0 4 taken 
up with water and the solution filtered on the same filter with 
the main portion for the determination of Pb and Cu. A little 
Fe and a considerable amount of A 1 will be added to the sample 
from the crucible, so that this portion cannot be used for them. 

The alkaline filtrate from the sulfur and soda fusion contains 
all of the Sb in an ordinary bronze, and some of the As. If the 
Sb is more than one-eighth as much as the Sn, this method 
should not be trusted for it, but it will have to be determined on 
this portion as well, in order to correct the Sn determination. 
The same is true of the As. The solution will also contain the 
P. This is generally determined on a separate portion, but it can 


SEPARATIONS 


147 


be taken from this. If it is necessary to do so, acidulate the 
solution with HC 1 , filter, add 0.2 gram of Fe to the filtrate, in 
the form of a ferric salt, precipitate the Fe, and determine P 
as in the analysis of steel. The sulfide precipitate should be dis¬ 
solved in stock alkali. 

To the alkaline solution containing the Sn, Sb, and As, add 
an excess of KC 10 3 and HC 1 with stirring until the sulfides are 
decomposed. No heat should be applied and just enough acid 
added to decompose the chlorate slowly. Then add enough HC 1 
to decompose the rest of the KC 10 3 , boil out the Cl and concen¬ 
trate the solution to give half strength HC 1 , filter the solution on 
an asbestos filter (page 14) and wash with an equal volume of 
concentrated HC 1 , pass H 2 S and precipitate As 2 S 5 , filter on a 
weighed Gooch crucible and wash with 60 per cent HC 1 , then 
once with water, dry and weigh as As 2 S 5 . Concentrate the fil¬ 
trate to 75 cc. and determine Sb by the bromate method. 

Calculate P to P 2 O s , As to As 2 O s , and Sb to Sb 2 0 4 , add the 
oxides already determined and deduct the sum from the ignited 
tin precipitate. The difference is Sn 0 2 . If this method is car¬ 
ried out carefully it is the most accurate known for the complete 
analysis of bronze. It has the advantage that the major elements 
are all determined on the same portion, so that the footing will 
show whether the results are accurate in the frequent cases 
where duplicates disagree owing to unevenness in the sample. 
The remaining solutions are available for the determination of 
all the other elements except Fe and Al. It may be noted that Ti 
is also introduced into the solution from the porcelain crucible 
fusion. 

Volumetric Tin from the Metastannic Acid Precipitate.—When 
Sn is determined in bronze, it is often necessary to determine also 
Cu, Pb, and Zn, but not Sb or As. For this purpose the volu¬ 
metric method is easier than the gravimetric. 

Obtain the metastannic acid precipitate as in the gravimetric 
method, transfer it to an iron crucible, ignite, mix well with five 
to eight grams of Na 2 0 2 and fuse. Leach with water, add 65 cc. 
of HC 1 , keep the solution hot until all iron scales have dissolved, 


148 


NOTfJS ON CHEMICAL ANALYSIS 


transfer the solution to a flask, reduce with nickel and titrate 
with iodine. (Page 113). 

Lead, Copper, Zinc and Nickel in Bronze.—Proceed as in the 
gravimetric analysis, evaporate the filtrate from the metastannic 
acid to about 50 cc., add 10 cc. of H 2 S 0 4 (page 75) evaporate 
to fumes, take up, boil, and cool. 

Instead of weighing the residue insoluble after the sulfur 
and soda fusion, destroy the paper with acid, using 5 cc. of 
H 2 S 0 4 . Dilute this, boil and cool. Filter the two H 2 S 0 4 solu¬ 
tions through the same filter, using the smaller as a washing 
for the larger, into an electrolysis beaker, add 7 cc. of HN 0 3 , 
and electrolyse. If the apparatus available will not accommodate 
the quantities here described, the whole determination can be 
done on a smaller scale, using one or two grams of the sample. 

Dissolve the PbS 0 4 and convert it to chromate. 

In taking down the electrodes, it is better to allow a little Cu 
to dissolve than to lose any of the solution or to dilute it much. 
The best way is to plug out the current, drop the beaker, put 
another under the electrodes and wash them with a wash-bottle. 
Then they can be rinsed in more water and dried with alcohol 
or acetone. The electrolysis beaker is emptied into the one used 
for the first rinsing, which having a lip is more convenient for 
filtering. 

Pass H 2 S into the cold solution. The precipitate will contain 
what Cu was lost from the electrode, and some Sn. This is 
partly from the fused Sn 0 2 , and cannot be used as a correction 
on the volumetric Sn. Ignite the precipitate, dissolve out the 
Cu with HN 0 3 , take it up with water and NH 4 OH and determine 
Cu by color. (Page 120). 

Boil the H 2 S out of the filtrate, add NH 4 OH and (NH 4 ) 2 S 2 O g , 
precipitate Fe, Al, and Mn and filter. Wash with the solution 
used for Zn in ores. The precipitate may be used for Mn and 
Fe, but will give slightly high results for Fe. 

Neutralize the filtrate with HC 1 and make it just acid. If 
the acid is added drop by drop with stirring until a piece of 
litmus paper is seen to change from purple to dull red, and then 


separations 


149 


with another drop to bright red, the conditions are right for 
the separation. 17 

Pass H 2 S for 15 minutes and let the solution stand cold until 
it settles, or over night. Filter on an eleven-centimeter paper 
with pulp, and wash beaker and paper once with cold water, 
filling the filter. Return the paper and precipitate to the beaker, 
add 10 cc. of water, 7 cc. of HC 1 , dissolve the ZnS, add ten 
grams of NH 4 C 1 , dilute and titrate by Tow’s method. 18 . 

Add HC 1 to the filtrate, boil out the H 2 S and precipitate the 
Ni as glyoxime. 

Iron and Aluminium in Bronze.—Weigh five grams into an elec¬ 
trolysis beaker, add 25 cc. of water, 10 cc. of H 2 S 0 4 , and, cau¬ 
tiously, 10 cc. of HN 0 3 . Put the beaker on a cold or warm stove 
and gradually increase the heat, boil out red flames, dilute and 
electrolyse. Transfer the electrolyte to an ordinary beaker, add 
10 cc. of HC 1 , boil until the solution is clear, dilute and separate 
Sn by H 2 S, boil out and oxidize the solution and precipitate Fe 
and A 1 together with NH 4 OH. Wash the precipitate with 
NH 4 C 1 solution to remove Zn, and then wash both beaker and 
precipitate thoroughly with hot water to remove chlorides. If 
the precipitate is large it is best to dissolve it in H 2 S 0 4 and re¬ 
precipitate to make sure that nitrates are removed. Dissolve the 
precipitate with 10 cc. of 20 per cent H 2 S 0 4 , pass the solution 
through the reductor, preferably a small one, and titrate the Fe. 

Precipitate Fe and A 1 in the solution after titration by the 
basic acetate method, bringing the solution to exact neutrality 
by dilute NH^OH and adding no extra acetic acid but only a 
gram of acetate, to make sure that all A 1 is precipitated. Filter 
and wash slightly. 

Stopper the lower end of the funnel with a rubber plug made 
by boring a stopper, and sharpened on an emery wheel. Make 
up a hot 20 per cent H 2 S 0 4 solution, measure out 2 cc. and pour 
it drop by drop around the top of the filter, stirring with the rod 
until the precipitate dissolves. Now remove the plug and let 
the solution run into the beaker. Before washing the filter use 

it Treadwell. “Quantitative Analysis.” Scott. “Standard Methods.” 

18 I,ow. “Ore Analysis.” 


NOTES ON CHEMICAL ANALYSIS 


150 

the filtrate to dissolve all of the precipitate that remains on the 
sides of the beaker. Wash into the electrolytic apparatus with 
a mercury cathode and electrolyse to remove Fe. 19 

The rotating anode is unnecessary in the use of the mercury 
cathode, if time enough is given, and as it is not to be weighed, 
the apparatus is easily made. An ordinary tumbler with a hole 
bored in the side at the bottom, a wire introduced through a 
rubber plug, and enough mercury inside to cover the wire, makes 
the cell and the cathode. The anode is made of a platinum wire 
bent into a horizontal coil with the riser at the side, so that a 
cover glass with a notch in the side will cover the beaker. The 
volume of the solution should be about 100 cc. and the current 
from one-tenth to one ampere. 

Fe does not dissolve out of the mercury in the very dilute 
acid when the current is stopped, so that no special device is 
necessary for quick disconnection. The solution is filtered away 
from the mercury, by decantation as much as possible. Add 
10 cc. of HC 1 to the filtrate, neutralize with NH 4 OH, boil, and 
let the solution stand to settle. A trace may not show itself 
at once. 

If the sample contains P, it will be found with the A 1 as 
A 1 P 0 4 . If it is in excess over the A 1 the precipitate may be 
assumed to be of that composition. It may be advisable to pre¬ 
cipitate all the A 1 as A 1 P 0 4 by the addition of more phosphate 
before the neutralization, but generally the quantity is so small 
that it makes little difference how it is weighed. All that is 
needed is to know that it is below a certain percentage. 

SEPARATION OF THE ALUMINIUM GROUP 

After the H 2 S group has been separated, the solution must 
be oxidized in such a way as to leave nothing that will precipi¬ 
tate Mn 0 2 in an alkaline solution. Peroxides and persulfates 
cannot be used for this purpose, as they do not boil out of an 
acid solution. Aqua regia will do. If either HNO s or HC 1 is 
already in the solution enough of the other acid may be added. 
There should be at least 2 cc. of HNO s and 8 cc. of HC1 to 
make sure of oxidizing the Fe in an ordinary ore analysis, and 

19 Smith. “Electro-Analysis.” 


separations 


51 


the solution should be boiled for a few minutes. It is best to 
boil out all the H 2 S and have a clear solution before making the 
oxidation, or S will precipitate. 

As the ordinary ore contains both Fe and Al, and as Cr is 
comparatively rare, the basic acetate separation adapted to Al 
is most commonly used. 

Basic Acetate Precipitation.—This has already been described 
on page 104, in the way that it should be used in quantitative 
analysis. Before neutralizing, the solution should be concen¬ 
trated to 100 ce. or less and should be cold, as this makes it 
easier to get the neutral condition. 

As the washing of this precipitate is difficult, it is easier to dis¬ 
solve it in HC 1 or H 2 S 0 4 and repeat the separation than to try 
to wash out all of the unprecipitated elements. There may also 
be some occlusion which washing will not break up. Reprecipita¬ 
tion should be practiced whenever the Ni or Co color is visible, 
and when the amount of Ca is large enough to give a brisk 
evolution of C 0 2 when the fresh sample is treated with HC 1 . The 
filtrates should be evaporated during the subsequent precipita¬ 
tions, so that they can eventually be combined in one beaker. 

After the basic acetate separation, the precipitate is dissolved 
in dilute H 2 S 0 4 . Dilute it to about half the final volume used 
for the basic acetate separation, put in a piece of litmus paper 
and add NH 4 OH until the solution is barely alkaline. Boil and 
smell the steam. When the odor of NH 3 is barely perceptible 
the solution is neutral. Remove it from the heat, add the pulp 
of an ashless filter large enough to hold the precipitate, stir it in 
and let it settle. Filter and wash well with hot water. Com¬ 
bine all the filtrates, add NH 4 OH in slight excess, and boil them 
down to about 400 cc. If any Al(OH) 3 separates, filter it, wash 
it well with hot water, and add it to the main precipitate. 

If the main precipitate cannot be rubbed out of the beaker 
completely, use a piece of ashless paper moistened with 1 per 
cent H 2 S 0 4 . This will loosen without dissolving it. Place the 
wet precipitate and paper in a weighed porcelain or platinum 
crucible. Silica should not be used, as it cracks after the bisul¬ 
fate fusion. 


152 


NOTES ON CHEMICAL ANALYSIS 


Roast off the paper and ignite uncovered with the crucible 
slanting and the flame at the back, so that fresh air can reach the 
precipitate. After the carbon is all burned off, apply the blast 
lamp, using an oxidizing flame, with the crucible first uncovered 
and then covered, so as to dehydrate the A 1 as much as possible 
and reduce the Fe as little as possible. Weigh and repeat the igni¬ 
tion to constant weight. The effect of the paper pulp is to leave 
the ignited residue fine and flaky, easily dehydrated and easily 
fusible, instead of being in hard lumps as it otherwise would be. 
The ignited precipitate consists of A 1 2 0 3 , Fe 2 O s , Ti 0 2 , and P 2 0 5 . 
Fuse it with bisulfate as described on page 81. After leaching 
the fusion, if there is an insoluble residue, filter, ignite and fuse 
it in a small amount of bisulfate. It it still does not dissolve, 
make other tests to find out what it is. 

Pour the clear solution through the reductor and titrate it 
with KMn 0 4 . Add a drop of H 2 0 2 if the reagent is free from 
P, or else use Na 2 0 2 , and determine Ti by color comparison 
with a standard solution. 20 As much as 0.005 gram of Ti 0 2 
may be disregarded so far as its effect on the Fe titration is 
concerned, but it must be counted in the analysis of the pre¬ 
cipitate. If there is a larger amount of Ti, the determination of 
Fe must be modified. 

The Fe is first reduced by H 2 S and titrated. (Page 122.) 
Then the reductor is equipped with a tube leading to the bottom 
of the flask and enough ferric sulfate solution put in to give a 
proportionately large excess over the Ti, with enough solution 
for the end of the tube to dip two or three centimeters under the 
surface. The density of the solution must be decidedly less than 
that containing the sample, so that the latter will stay under. 

The sample should contain about 10 per cent of free H 2 S 0 4 , 
so that it will evolve H freely in contact with the Zn. Start the 
reductor with some 10 per cent acid to clear all the air out of 
it and replace it with H. Then pass the sample in slowly, so 
that it will take about ten minutes to go through. Follow with 
10 per cent acid and then water, so that the Ti shall be in an 
atmosphere of H until it has been mixed with the ferric solu- 


2(1 Low. “Ore Analysis.’’ 


separations 


153 


tion. Ti will reduce its equivalent of Fe, which does not oxidize 
so quickly in the air, so that the titration is conducted in the 
same way as for Fe alone. 

Before titrating, see that the Ti solution has been well mixed 
with the other. The H may do it, but it is well to make sure. The 
titration figure, less that obtained for the H 2 S reduction, gives 
that for Ti. 21 

Phosphates.—If the special Ti titration has been made, it is as 
well to depend on a separate P determination. If not, some time 
may be saved by getting the P from the solution after titrating. 
Make a rough basic acetate precipitation to separate the Mn, 
dissolve the precipitate in 18 cc. of HN 0 3 , filter it into a 400 cc. 
beaker, add 15 cc. of NH 4 OH, dilute to 150 cc. and at a tempera¬ 
ture of 40 to 50° add 40 cc. of ammonium molybdate. 22 

Stir occasionally for ten minutes and let stand for an hour. 
Filter on a weighed Gooch crucible and wash with 2 per cent 
HN 0 3 . Dry at ioo° if the precipitate is small, or at no° if it 
is large. The weight times 1.63 equals P. 23 By subtraction the 
weight of A 1 2 0 3 is found. 

Separation of Uranium from Interfering Elements.—All U 

minerals are soluble in acids. As the H 2 S 0 4 solution is prefer¬ 
able later, start with HNO s and expel it with as little H 2 S 0 4 
as will give a liquid excess, not more than 5 cc. Enough of the 
sample should be taken to contain about 0.25 gram, unless the 
percentage is very low. Five grams is the ordinary amount for 
commercial ores. 

Destroy organic matter if the material contains it, by repeated 
additions of HNO s , finally expelling all HNO s . Take up with 
water, pass H 2 S and filter. Boil out H 2 S. 

Add Na 2 0 2 to the cold filtrate to oxidize Fe and V. Then 
add Na 2 CO s a little at a time with stirring until the solution is 
alkaline and there is a gram or two of undissolved carbonate. 
Add a little Na 2 0 2 from time to time during the neutralization 
to keep the V red, if it is present. 

Boil the solution for fifteen minutes, add ten grams of (NH 4 ) 2 - 
S 0 4 , allow the solution to cool somewhat and filter. The sodium 

21 Gooch. “Methods in Chemical Analysis.” 

22 Blair. Scott. 

2 «Blair. “The Chemical Analysis of Iron.” 


154 


NOTES ON CHEMICAL ANALYSIS 


carbonate treatment is the best way to precipitate Fe, and the 
conversion later to the ammonium salt helps to precipitate Al. 
The precipitation of Al is not complete, and should not be. 
Dissolve the precipitate and repeat the precipitation. If the 
second filtrate shows a yellow color, make a third separation. 
Combine the filtrates, add H 2 S 0 4 in excess ,and about five grams 
of (NH 4 ) 2 HP 0 4 and boil out the C 0 2 . Add to the hot solu¬ 
tion, which should be about 400 cc., slightly dilute NH 4 OH in 
excess. Then add acetic acid until litmus paper shows red, not 
more than 1 cc. excess. When cool, filter with pulp. 

U by itself makes a difficult precipitate to filter, but the pres¬ 
ence of a little Al coagulates it and makes filtration easier. Wash 
the precipitate with a cold solution of ammonium sulfate and 
acetate, slightly acid. 

In the neutral solution, U and V are precipitated together, 
but if a phosphate is present in excess in the acid solution the 
U prefers it and leaves the V in solution. Under these con¬ 
ditions, however, V is only slightly soluble, and may form dense 
orange crystals which dissolve slowly in the washing solution. 

Dissolve the precipitate in hot dilute H 2 S 0 4 and test for V 
with H 2 0 2 . If there is the slightest trace, the precipitation must 
be repeated. Add two grams of the phosphate, dilute with hot 
water, and add ammonia and acetic acid as before. 

After V is separated, dissolve with 10 cc. of H 2 S 0 4 , filter 
into a 400 cc. beaker, and evaporate to fumes. At the first 
appearance of fumes remove the beaker and add small particles 
of KMn 0 4 in excess to destroy organic matter. Take up with 
water, pass the solution through the reductor under the same 
conditions as are suitable for Fe, shake the flask for one minute, 
and titrate. The accurate determination of the end correction in 
this determination is important. 

Separation of Much U from Little Impurities.—Use a large 
weight, five to ten grams. Dissolve in HNO s , pass H 2 S, filter, 
boil out H 2 S, add (NH 4 ) 2 C 0 3 in excess, so as to dissolve all U, 
and then a little NH 4 SH. Let the solution stand until the pre¬ 
cipitate settles, preferably over night. Filter and wash with the 
same reagents. Repeat the separation if it appears to be neces- 


SEPARATIONS 


155 


sary. Acidulate the filtrate, boil out H 2 S, take an aliquot which 
contains about .25 gram of U 3 O s , add 5 cc. of H 2 S 0 4 and 
NH 4 OH in excess. Warm until the precipitate settles and filter 
with pulp. Wash with hot (NH 4 ) 2 S 0 4 solution, ignite in a 
porcelain crucible, using the full heat of the Bunsen flame, and 
weigh. 

Dissolve the residue in the crucible with a little HN 0 3 . Filter 
if there is an insoluble residue of Si 0 2 and weigh the residue. 
Keep the volume of the filtrate down as much as possible. Add 
(NH 4 ) 2 iCO s in slight excess, warm slightly, and if a precipitate 
collects, filter and weigh it as Al 2 O s . Acidulate and concentrate 
the filtrate and test with H 2 G 2 for V. If any appears, determine 
it by comparison with a standard solution of V. Calculate it to 
V 2 0 5 . Deduct the impurities, and report the difference as U 3 O s . 


INDEX 


Page 

Acetic acid, reagent . 69 

Alloy dissolving mixture .77, 91 

Alkali stock solution .64, 98 

Alloys, decomposition of .75-78, 91, 93 

Aluminium, properties . 54 

— identification ..... 106 

— determination .123, 152 

— dissolving . 78 

— group separations .105, 150 

— in bronze . 149 

Ammonia water, reagent . 63 

Ammonium acetate solution. 92 

— salts, reagent . 63 

Antimony, properties . 46 

— identification . 103 

— determination .ill 

— in bronze . 138 

— in ores . 134 

— from Pb and Fe .•. 135 

— little, from much Sn. 144 

Apparatus . 6 

Aqua regia . 76 

Arsenic, properties . 45 

— identification .97, 98, 102 

— determination .no, in 

— separations .130-134 

Asbestos filters . 14 

— choice of . 15 

Balance, chemical . 25 

Barium, properties . 6 1 

— identification . 95 , 108 

— in Pb assay . *39 

Basic acetate separation .104, 151 

Beaker tongs . *9 

Bismuth, properties . 5 2 

— identification . too 

— determination . 

— in Pb assay . *38 

— little, from much Pb. 1 4 2 

— little, from much Sb. : 42 


n 











































158 NOTES ON CHEMICAL ANALYSIS 

Page 

Bismuth (Continued) 

— from usual impurities . 142 

— from Te . 14 3 

— water precipitation . 101 

Bisulfate fusion . 81 

Boron, properties . 4 1 

Bromine, properties . 44 

— and bromides, reagent . 68 

Bronze, separation of Pb, Cu, Ni and Zn . 148 

— separation of Fe, A 1 and P. 149 

Burettes, calibration and use . 27 

Cadmium, properties . 53 

Cadmium identification . 101 

— determination . 121 

— from much Zn . 143 

Calcium, properties # . 60 

— identification . 108 

— determination . 127 

— in Pb assay . 139 

Calculations, tabulation method . 34 

— geometrical . 39 

Calibration of glassware .27, 33 

Carbon, properties . 41 

Chlorates, reagent . 68 

Chlorides, reagent . 67 

Chlorine, properties . 44 

Chromium, properties . 55 

— identification . 107 

— determination . 124 

Cobalt, properties . 59 

— identification . 108 

— determination . 127 

— from Ni . 108 

Copper, properties . 52 

— identification . 101 

— determination .119-121 

— in bronze . 148 

— in ores . 136 

— from much Sn and Sb . 136 

— little, from much Sn . 144 

— sulfocyanate separation . 136 

Correction for scale . 40 

Crucible lifter . 18 

Cyanides, reagent . 70 













































INDEX 


159 

Page 

Decantation, washing by . y^ 

Decomposition of alloys . 72 

— of alloys and salts . 

— ° f °, res ...'.'."V '.'78,93 

— of slags and silicates ... 79 

Evaporating in flasks . 2 ^ 

Evaporation of solutions . 72 

Filter rack . 5 

Filtering . 72 

Filters, setting .. I2 

— choice of . !2 

— paper . ?2 

— reinforced . !4 

— asbestos, in funnel .. 14 

Flask cover for evaporation. 23 

— tongs . 19 

Flasks, calibration of . 29 

Fluorine, properties . 44 

Funnels, shape of . 12 

Fusion methods .81-86 

— mixture . 83 

Glass, old, making fusible . 1 

Glass-working . 1-6 

Gooch crucible . 14 

— crucible holders . 16 

Hydriodic acid, reagent . 69 

Hydrochloric acid, reagent .67, 75 

Hydrofluoric acid, reagent . 66 

Hydrogen, properties . 41 

— sulfide generator . 9 

— sulfide precipitation . 95 

— sulfide test . 97 

Hydrosulfuric acid, reagent . 69 

Iodides, reagent . 69 

Iodine, properties . 45 

Insoluble residues, treatment of .80, 94 

Iron, properties . 57 

— identification . 105 

— determination . 122 

— in bronze . 149 

— little, from much Sb . 135 

— little, from much Sn . 135 


12 












































l6o NOTES ON CHEMICAL ANALYSIS 

Page 

Lead, properties . 5 1 

— identification . 100 

— determination .115-118 

— in alloys . *40 

— in impure metallic mixtures .• • • I 4 I 

— in bronze . I 48 

— in ores and waste materials . 138 

— little, from much Sb .< • 135 

— little, from much Sn . 135 

— separation as PbCl 2 . 140 

— separations . r 38 > 139 

— chloride, separation .76, 9 1 

— chloride, solubility . 5 1 

Lithium, properties . 62 

— identification . 109 

Magnesium, properties . 60 

— identification . 108 

Manganese, properties . 58 

— identification . 107 

Marking glazed surfaces .15, 21 

Mercury, properties . 50 

— identification . 99 

Metastannic acid precipitate, analysis . 145 

— acid precipitate volumetric Sn in . 147 

Molybdenum, properties . 49 

— identification . 97 

— determination . 97 

— from Sn, Sb, As, Se and Te . 102 

Mouthpiece . 23 

Nickel, properties . 59 

— identification . 108 

— determination . 127 

— from Co . 108 

— in bronze . 148 

Niter and soda fusion . 83 

Nitric acid, reagent .65, 77 

Nitrogen, properties . 41 

Ores, acid decomposition .78, 79, 93 

— fusion methods .81, 86 

Organic matter, destroying by acid . 74 

Oxalic acid and oxalates, reagent . 70 

Oxides, dissolving.79, 93 

Oxidizing mixtures . 77 

Oxygen, properties . 41 














































INDEX l6l 

Page 

Paper pulp .12, 13 

Pencils for glass and porcelain .15, 21 

Phosphorus, properties . 43 

— identification . 106 

— determination in A 1 precipitates . 153 

Pipette, dipping . 24 

Pipettes, calibration and use . 28 

Policemen . 21 

Potassium, properties . 61 

— identification . 109 

— bromate titration . 113 

— salts, reagent . 64 

Pouring bottle . 22 

Precipitation .71, 74 

Properties of elements . 41 

Pulp, paper, use of.12, 13 


Qualitative analysis 


87-109 


Reprecipitation 
Residue, insoluble . 
Rubber stoppers ... 
— tipped rods 


• 74 

80, 94 

20 

21 


Selenium, properties . 

— from Te . 

Silicates, dissolving by acid 

Silicon, properties . 

Silver, properties . 

— identification . 

Slags, decomposition . 

Sodium, properties . 

— identification . 

— carbonate fusion . 

— hydroxide fusion . 

— peroxide fusion .. 

— salts, reagent . 

— stannite, reagent . 

Stock alkali solution . 

Strontium, properties . 

— identification . 

Sulfides, reagent . 

— decomposition of . 

Sulfur, properties . 

— and soda fusion .. 

Sulfuric acid, reagent . 


. 48 

• 103 

• 79 

. 42 

. So 
.. 100 

79 
61 

,. 109 

.. 82 

.. 86 
.84, 94 
.. 64 

.. 100 

.64, 98 
61 

108, 95 
.. 69 

. 78 , 93 
.. 42 

.. 85 

. 64 , 78 













































162 notes on chemical analysis 

Page 

Tabulation method for direct ratios . 34 

Tartaric acid, reagent . 69 

Tellurium, properties . 49 

— from Se . 103 

Tin, properties .. 47 

— identification . 103 

— determination .103, 113 

— from Fe and Pb . 135 

— in lead assay . 139 

— oxide, ignition . 145 

— separations .129, 136 

— volumetric, from metastannic acid precipitate, . 147 

Titanium, properties . 57 

— identification . 106 

— determination . 152 

Tongs for beakers and flasks . 19 

Tungsten, properties . 43 

— identification .93, 94 

Uranium, properties . 55 

— identification . 107 

— determination . 125 

— separations . 153 

Vanadium, properties . 56 

— identification . 106, 107 

— determination . 124 

Volumetric apparatus calibration table . 29 

Wash bottles . 9 

Washing precipitates .72, 73 

Water overflow system . 9 

Weights, adjusting . 26 

Zinc, properties . 59 

— identification . 108 

— determination . 125 

— from Ni and Co . 107 

— in bronze . 148 






































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